Four Common X-Ray Procedures:

Problems and Prospects for Economic

Evaluation

April 1982

NTIS order #PB83-165506
THE IMPLICATIONS OF

COST-EFFECTIVENESS

ANALYSIS OF

MEDICAL TECHNOLOGY

APRIL 1982

BACKGROUND PAPER #5: FOUR COMMON X-RAY

PROCEDURES: PROBLEMS AND PROSPECTS

FOR ECONOMIC EVALUATION

by

Judith L. Wagner, Ph. D., and Martha J. Krieger

The Urban Institute, Washington, D. C.

 OTA Background papers are documents containing information that supplements

formal OTA assessments or is an outcome of internal exploratory planning and

evaluation. The material is usually not of immediate policy interest and does not

 present options for Congress to consider.

. i
Library of Congress Catalog Card Number 82-600532

For sale by the Superintendent of Documents,

U.S. Government Printing Office, Washington, D.C. 20402
Foreword

This volume is a background paper for OTA’S assessment, The Implications of

Cost-Effectiveness Analysis of Medical Technology, Prepared at the request of the

Senate Committee on Labor and Human Resources, that assessment analyzes the feasibility, implications, and usefulness of applying cost-effectiveness and cost-benefit analysis (CEA/CBA) in health care decisionmaking. The major, policy-oriented report of

the assessment was published in August 1980, In addition to the main report and this

paper on the economic evaluation of diagnostic X-ray procedures, there are four other

background papers: 1) a document which addresses methodological issues and reviews

the CEA/CBA literature, 2) a psychotherapy case study, 3) 17 other case studies of individual medical technologies, and 4) a review of international experience in managing

medical technology. Another related report was published in September of 1979: A Review of Selected Federal Vaccine and Immunization Policies.

Background Paper #.5: Four Common X-Ray Procedures: Problems and Prospects

for Economic Evaluation was specifically requested by the Senate Committee on Finance. It was prepared under contract for OTA by Judith L. Wagner, Ph. D., and Martha J. Krieger, of the Urban Institute.

Since OTA does not make specific recommendations of policy action or endorse

particular technologies, the views presented in this study are strictly those of the

authors. OTA encouraged the authors to present balanced information and also subjected the study to an extensive review process. Initial drafts were reviewed by OTA

staff and members of the advisory panel for the overall assessment, and subsequent

drafts were then reviewed by more than 20 outside reviewers from Government agencies, professional societies, consumer and public interest groups, medical practice, and

academia. Although the many reviewers for this background paper and the other parts

of the assessment cannot be acknowledged individually, OTA is very grateful for their

comments and advice.

Director

I l l
Advisory Panel on The Implications of

Cost-Effectiveness Analysis of Medical Technology

John R. Hogness, Panel Chairman

President, Association of Academic Health Centers

Stuart H. Altman Sheldon Leonard

Dean Manager

Florence Heller School Regulatory Affairs

Bratzdeis University General Electric Co.

James L. Bennington

Chairman

Department of Anatomic Pathology and

Clinical Laboratories

Children’s Hospital of San Francisco

John D. Chase

Associate Dean for Clinical Affairs

University of Washington School of Medicine

Joseph Fletcher

Visiting Scholar

Medical Ethics

School of Medicine

University of Virginia

Clark C. Havighurst

Professor of Law

School of Law

Duke University

Barbara J. McNeil

Department of Radiology

Peter Bent Brigham Hospital

Robert H. Moser

Executive Vice President

American College of Physicians

Frederick Mosteller

Chairman

Department of Biostatistics

Harvard University

Robert M. Sigmond

Advisor on Hospital Affairs

Blue Cross and Blue Shield Associations

Jane Sisk Willems

VA Scholar

Veterans Administration

iv
OTA Staff for Background Paper #5

H. David Banta, Assistant Director, OTA

Health and Life Sciences Division

Clyde J. Behney, Health Program Manager

Clyde J. Behney, Project Director, Implication of Cost-Effectiveness

Analalysis of Medical Technology

Kerry Britten Kemp, * Editor

Virginia Cwalina, Research Assistant

Lorraine Ferris, Secretary

Nancy L. Kenney, Secretary

OTA Publishing Staff

John C. Holmes, Publishing Officer

John Bergling Kathie S. Boss Debra M. Datcher Joe Henson

9

0TA contract personnel
AUTHORS’ ACKNOWLEDGMENT

The authors of this background paper benefited from an earlier paper prepared by David Collier,

M. D., for the Office of Technology Assessment. That paper was most helpful in directing the authors

to the pertinent literature and providing summaries of the research field.

vi
Contents

Introduction ....,... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Cost-Benefit and Cost-Effectiveness Analysis in the Evaluation of

Diagnostic X-Ray Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Organization of This Background Paper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Summary of Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2. EVALUATION MODELS

Studies of Diagnostic Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Studies of Diagnostic Yield. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Studies of High-Yield Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Studies of Diagnostic Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Studies of Outcomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3. CHEST X-RAY

Utilization, Cost, and Controversies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Chest X-Ray Evaluations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Studies of Community-Based TB Screening Programs . . . . . . . . . . . . . . . . 20

Lung Cancer Screening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Studies of Chest X-Ray Screening of Selected Patient Populations. . . . 23

Studies of Patient Management and Followup. . . . . . . . . . . . . . . . . . . . . . . 26

Studies of the Diagnostic Uses of Chest X-Ray . . . . . . . . . . . . . . . . . . . . . . 26

Studies of Radiological Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4. SKULL X-RAY

Utilization, Cost, and Controversies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Skull X-Ray Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Diagnostic Efficiency of Skull X-Ray Examinations . . . . . . . . . . . . . . . . . . 32

High-Yield Criteria [or Skull X-Rays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

5. BARIUM ENEMA

Utilization, Cost, and Controversies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

The Diagnostic Efficiency of BE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

High-Yield Criteria force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

6. EXCRETORYUROGRAM

Utilization, Cost, and Controversies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5

Diagnostic Yield and High-Yield Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Studies of Appropriate Radiologic Method . . . . . . . . . . . . . . . . . . . . . . . . 47

Studies of the Role of ExU in Screening for

Renovascular Hypertension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Studies of the Diagnostic Information From Ecu . . . . . . . . . . . . . . . . . . . . 49

APPENDIX A: GLOSSARY OF TERMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

APPENDIX B: DESCRIPTION OF OTHER VOLUMES

OF THE ASSESSMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Vll
List of Tables

Table No. Page

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

Estimated Number of Diagnostic X-Ray Procedures in the United States,

1970 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Average Amount Billed by Radiologists for

California Medicaid Program, 1975. . . . . . . .

Medicaid Chest X-Ray Claims in California

First Quarter of 1978, by Location of Service

Medicaid Chest X-Ray Claims in California

First Quarter of 1978, by Location of Service

Screening for Tuberculosis . . . . . . . . . . . . . . .

Screening for Lung Cancer . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Selected X-Ray Procedures,

. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Submitted by Physicians in

. . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Submitted by Radiologists in

. . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

. . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

,... . . . . . . . . . . . . . . . . . . . . . . . . 22

Chest X-Rays for Selected Patient Populations . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Medicaid Skull X-Ray Claims in California Submitted by Physicians in

First Quarter of 1978, by Location of Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Medicaid Skull X-Ray Claims in California Submitted by Radiologists in

First Quarter of 1978, by Location of Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Medicaid Barium Enema Claims in California Submitted by Physicians in

First Quarter of 1978, by Location of Service. . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Medicaid Barium Enema Claims in California Submitted by Radiologists in

First Quarter of 1978, by Location of Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

The Sensitivity of Barium Enema in the Detection of Polyps . . . . . . . . . . . . . . . 40

Medicaid Excretory Urogram Claims in California Submitted by

Physicians in First Quarter of 1978, by Location of Service . . . . . . . . . . . . . . . . 46

Medicaid Excretory Urogram Claims in California Submitted by

Radiologists in First Quarter of 1978, by Location of Service.. . . . . . . . . . . . . . 46

. Vlll
1 .

Overview and Summary
1 .

Overview and Summary

INTRODUCTION

This paper is about the

of diagnostic procedures.

about whether and when

diagnostic procedure are

costs.

economic evaluation

To be precise, it is

the benefits from a

worth its risks and

The issue of economic evaluation is explored

in the context of four common diagnostic X-ray

procedures that together in 1970 accounted for

almost half of all diagnostic X-ray examinations

in the United States:

● the chest X-ray,

• the skull X-ray,

• the barium enema study, and

• the excretory urogram.

Since these are all long-established and widely

used radiological procedures, evidence of their

benefits, risks, and costs should be as comprehensive as that of most other diagnostic procedures. The methods used to evaluate these

procedures should (and do) represent the general

state-of-the-art in the assessment of most diagnostic technologies.

The four X-ray procedures are also interesting

in their own right. As high-volume procedures,

they use up substantial health care resources.

Table 1 summarizes the findings of a 1970 survey

of diagnostic X-ray procedure use in the United

States. Of the 130 million diagnostic X-ray procedures performed in that year, 60 million were

for the four procedures of interest here. The

average amount billed by a sample of radiologists in California in 1975 for each of the four

procedures is shown in table 2. Though billed

charges overstate the amount actually received

and data from California do not represent the

nation, the total burden of expenditures for

X-rays is substantial.

The appropriateness of use of each procedure

has been the subject of intense debate within the

Table 2.—Average Amount Billed by Radiologists

for Selected X-Ray Procedures, California Medicaid

Program, 1975

Average

Procedure billed amount

Chest X-ray:

Single . . . . . . . . . . . . . . . . . . . . . . . . . . . . $13.03

Double. . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.73

Complete . . . . . . . . . . . . . . . . . . . . 31.61

Barium enema:

Colon, barium enema ... . . . . . 45.32

With air contrast . . . . . . . . . . . . . . . . . . . 64.29

Air contrast (independent procedure) . . NA

Excretory urogram:

Routine intravenous pyelography . 53.51

Extended hypertensive . . . . . . . . . . . . . . 59.60

Infusion, DIP. . . . . . . . . . . . . . . . . . . . . 70,00

Skull X-ray:

Limited series. . . . . . . . . . . . . . . . . . . . . 21.71

Complete (minimum of four views). . . 41.53

.

NA = not avallabie

SOURCE Urban Institute sample of approximately 5.0130 solo pract It loners, (n

cludlng 177 radiologists (32 6 Percent of the solo radiologists In

Call fornta)

Table l.— Estimated Number of Diagnostic X-Ray procedures in the United States, 1970 (in thousands)

Private office Average number of

Private Health agencies films per examination

Type of examination All Hospitals Radiologists Others groups and others (all sources)

All radiologic procedures 129,070 81,688 3,334 20,419 8,923 14,708 2,4

Skull . . 4,22 0 3,616 NA NA NA NA 4.03

Chest radiograp h 48,569 32,491 NA 7,565 3,207 4,293 1.7

Barium enema . . . . . . . 3,428 2,774 NA NA NA NA 3.!34

Excretory urogram . . ., 3,996 3,413 NA NA NA NA 5.31 —

NA = not ava!lable

SOURCE Department of Health, Education and Welfare Publlc Health Service. POpU/a$IOn Exposure 10 X Rays. U S 7970 November 1973 (301

3
4 ● Background paper #5: Four Common X-Ray Procedures: Problems and Prospects for Economic Evaluation

medical profession. These debates have virtually suits have contradicted prevailing patterns of

always been brought about by the findings of medical care. Thus, a critical review of the evalevaluative research. Indeed, evaluations of the uative research on each of the four diagnostic

benefits of these procedures seem to have raised technologies is a good way to characterize the

rather than answered questions about proper in- current controversies surrounding each of these

dications for their use, especially when the re- procedures.

COST-BENEFIT AND COST-EFFECTIVENESS ANALYSIS IN THE

EVALUATION OF DIAGNOSTIC X-RAY PROCEDURES

Cost-benefit analysis (CBA) and cost-effectiveness analysis (CEA) are methods to assist in

allocating scarce resources among alternative

uses. These methods were developed primarily

to evaluate large public-sector investments such

as highways, dams, and airports. When applied

to diagnostic procedures, they are intended to

provide information on two related questions:

1) Under what circumstances should the procedure be performed? and 2) How much investment in capacity to perform the procedure is

justified? The answer to the second question

rests on thorough study of the first, for only by

knowing when a procedure should be performed

can one assess how much investment in capacity

is justified.

Applying the principles to medical procedures, CBA would enumerate and place a value

on all benefits (both positive and negative) derived from performing a procedure on patients

with a specified set of conditions and would

compare those benefits to the cost of performing

the procedure. The resulting net social benefit

would indicate whether the procedure should be

performed under the specified conditions. In traditional CEA, a measure of procedure effectiveness would be designated, and the ratio of that

single measure to cost would be the critical item

for resource allocation. Lives saved, life-years

saved, quality-adjusted life-years saved, disability saved, and age-adjusted disability days saved

are measures of effectiveness often chosen in

studies of health care programs.

One can generalize the notion of economic

evaluation to a social accounting framework, in

which all dimensions of effect as well as cost are

identified and their values estimated. It is difficult to argue with the soundness of knowing the

direction and magnitude of all effects resulting

from the performance of a procedure on a particular patient. However, the ideal of comprehensive and accurate evaluation is seldom met

and may not be worth its own costs. Virtually

all good evaluative studies are limited in the dimensions of cost and/or effectiveness under investigation.

The critical weakness of most studies reviewed in this paper is that they fail to consider

one or more important implications of the procedure under study. By not dealing with these

important dimensions of effect or cost, they

leave open the possibility that their conclusions

will be criticized or, worse, ignored. Yet, the

paradox is that the conditions necessary to produce accurate information on the full array of effects and costs may not be achievable. The

methodological and ethical problems of evaluative research, as well as its costs, frequently

are barriers that cannot and perhaps even should

not be overcome.

ORGANIZATION OF THIS BACKGROUND PAPER

This background paper is divided into two ing studies of the four diagnostic X-ray proparts. The purpose of the first part is to sum- cedures and to lay out the strengths and weakmarize the different evaluative models underly - nesses of each method. That part also identifies
Ch. l—Overview and Summary ● 5

the conditions under which these models are

likely to provide information that can affect patterns of medical care. The second part of the

paper contains four separate chapters summarizing what is known about the utilization, costs,

risks, and benefits of each procedure, with particular emphasis on the evaluative methods employed.

The review of the evaluative literature of the

past decade is by no means comprehensive. To

be included here, a study must have provided

evidence pertaining to at least one ot the following two interrelated questions. Under what conSUMMARY OF FINDINGS

This study has provided insight into three important questions. What influence has the

evaluation literature had on the use of each of

the four diagnostic X-ray procedures? What factors limit the influence of evaluative findings on

medical practice? And, what directions might

evaluative research take to increase its influence

over medical decisionrnaking?

We cannot be precise about the influence of

the evaluative literature on medical practice, because data are unavailable on rates of use of

X-rays over time. But it is possible to infer from

the clinical literature whether a consensus has

developed in response to evaluative findings.

The influence of evaluative studies of X-rays in

screening (symptomatic) contexts appears to be

strong, but evaluations of X-rays in diagnostic

contexts, where patients present with complaints

or symptoms, seem to have little impact on medical standards or practice. In either context, the

more dramatic the results of the evaluation, the

more likely is the study to have an impact. For

example, studies demonstrating very low diagnostic yield of skull X-rays in emergency rooms

created general concern and have led to some

change in practice in a few centers (99,126).

The reasons for the limited influence of evaluations lie partly in the evaluative studies themselves and partly in the health care system.

Study methods often are so flawed that the reditions, if any, should a particular procedure be

performed? And, how should the procedure be

performed? Though many clinical studies address these kinds of issues, further conditions

were required of those included in the review:

measures of benefit, risk, or cost had to be specified explicitly; two or more alternative diagnostic strategies had to be compared either explicitly or implicitly; and a large enough number

of cases had to be analyzed to draw meaningful

inferences. The application of these additional

filters eliminated editorial opinions and case reports from the review.

suits cannot be trusted. Patient selection bias

due to uncontrolled study designs are a major

problem. Radiologic methods are often unstandardized. All too often, a procedure is evaluated

in a group of patients so heterogeneous in its

presenting signs, symptoms, and risk factors

that the results offer no guidance at all about

who should be X-rayed and who should not.

The evaluative criteria rarely include the ultimate benefits of the procedure. Time and time

again, as studies are reviewed in subsequent

chapters of this background paper, we conclude

that the study findings are inadequate because

the implications of the X-ray results for patient

health and well-being and for medical costs are

unknown.

A more fundamental barrier to the use of evaluation in decisions about X-rays lies in the conflict between the individual patient’s best interest

and society’s best interest. The individual patient, who seldom has to pay the full cost of the

procedure and often need not pay at all owing to

the availability of insurance or other third-party

payment, need not consider the costs against the

benefits of the examination. The public as a

whole, however, must make these tradeoffs.

This may explain why the results of evaluations

of X-ray screening programs are more influential

than are evaluations of diagnostic uses of X-ray.

Screening programs are often funded by public

health agencies, not by insurance coverage.
6 ● Background Paper #5: Four Common X-Ray Procedures: Problems and Prospects for Economic Evaluation

How can evaluations have a greater impact?

In the diagnostic context, investigators can begin

to consider the effect of the diagnostic strategy

on therapy and ultimately on patient outcomes.

Attention should be given to the clinical significance of missing disease if an X-ray is not ordered. Independently, research by economists

and social scientists on the reassurance value of

negative X-rays might put these benefits into

proper perspective. Greater care might be taken

in separating evaluations for patient groups with

different presenting conditions. The appropriate

level of aggregation of patient characteristics

should be considered explicitly in the study design. To this end, studies of the diagnostic yield

of X-ray and symptoms will be suggestive of patient groups where more thorough, outcome-oriented analysis is warranted.

Still, these new research directions will have

no effect on decisions about the use of X-rays

until both physicians and patients accept as

reasonable the possibility that the diagnostic

process might be truncated when the costs of

pursuing additional information outweigh its

potential benefits.
2.

Evaluation Model
2

Evaluation Models

To understand the strengths and weaknesses

of evaluation, one must keep in mind its fundamental purpose: to inform those who make decisions. The inferences drawn from an evaluative

study of a diagnostic procedure are important,

because they may influence decisions about its

use. Therefore, one must carefully examine the

assumptions underlying any approach to evaluation to determine the extent to which they provide direction or misdirection for decisions

about the use of a procedure.

Ideally, one would want an evaluative study

of a diagnostic procedure to provide precise

measurement of the full array of medical and

nonmedical benefits, risks, and costs resulting

from alternative diagnostic strategies applied to

a patient with specific signs, symptoms, and risk

factors. Additionally, the ideal study would provide some method for comparing one kind of

benefit or cost with another. Then, the decisionmaker could apply the findings in a relatively

straightforward fashion to choose among alternative strategies.

Reality is not so accommodating. No studies

of medical procedures deal with all possible benefits, risks, and costs. Nor do they often provide

a method for collapsing multiple dimensions of

benefit and cost into a single composite measure.

Often, they aggregate findings over patients

with diverse signs, symptoms, and risk factors,

thereby limiting their usefulness for diagnostic

decisions. Research costs, unfeasibility of measurement, and inability to make value tradeoffs

dictate that all evaluative studies stop far short

of the ideal. Yet, even partial approaches provide evidence that is useful. For example, most

studies of the four X-ray procedures discussed

here do not explicitly consider issues of cost, but

some do reach important findings about the

magnitude of the clinical benefits to be derived

from the procedure. Indeed, the most important

feature of diagnostic-procedure evaluation is not

whether it has considered all possible dimensions of benefit, risk, and cost but what it uses as

the “endpoint” of the evaluation (79). A study of

the cost or accuracy of diagnosis may carry a

message for medical decisionmakers that is quite

different from a study that chooses as its endpoint the patient’s ultimate health status or

costs.

In our review of the literature on the four

X-ray procedures, we were able to classify all

studies into one of five broad categories based

largely on their evaluative endpoints:

● studies of diagnostic “efficiency,”

● studies of diagnostic yield,

Ž studies of high-yield criteria,

● studies of diagnostic information, and

. studies of outcomes.

Each of these approaches is discussed in detail

below. Each has its advantages and disadvantages. One must consider an evaluative model in

terms of the cost and feasibility of anaIysis and

the reasonableness of the assumptions about factors outside its scope. In short, no single category of evaluation is best in all cases; each has a

place in the evaluator’s bag of techniques.

STUDIES OF DIAGNOSTIC EFFICIENCY

Diagnostic efficiency is used here to refer to would never occur: 1) the detection of disease

the capacity of a test to meet its immediate ob- when in truth none is there (false positives), and

jective: correct diagnosis, A perfectly efficient 2) the failure to detect disease when it exists

test is one in which either of two kinds of error (false negatives). A perfectly inefficient test

9
10 • Background Paper #5: Four Common X-Ray Procedures: Problems and Prospects for Economic Evaluation

would always be in error. Between these two extremes lie an infinite number of combinations of

frequency of the two kinds of error.

The classic measures of diagnostic efficiency

corresponding to each of the two errors are sensitivity and specificity. Sensitivity is the proportion of individuals with disease whose test results are positive (true-positive rate); specificity

is the proportion of normal individuals whose

test results are negative (true-negative rate).

Knowledge of these error rates is essential to

the appropriate interpretation of test results by

clinicians. Only by knowing the test’s sensitivity

and specificity and the prevalence of the suspected disease in the population can the clinician

accurately interpret a positive or negative finding on a test (55). Though probably no clinician

is prepared to perform sophisticated analyses of

pretest and posttest disease probabilities for

every test he or she orders, implicit processing of

such information does take place, and accurate

assessments of these two components of diagnostic efficiency in different situations are useful

in this regard.

The use of diagnostic efficiency to assist in the

choice among alternative diagnostic strategies is

another matter altogether. Here, we say that if

one test is both more sensitive and more specific

than another, it is more efficient and may be the

procedure of choice, although differences in the

cost of each test should also be considered before

such a decision can be made.

The comparison among tests is frequently not

so straightforward. The more sensitive test is

often less specific than its competitor. Then, it is

impossible to avoid considering the implications

of the two kinds of errors. If the consequences of

a false positive are major—perhaps the performance of expensive or risky followup tests or even

application of inappropriate and dangerous

therapy—high specificity is desirable. Conversely, if the implication of a false negative is

dire—the deterioration of the patient’s condition

to an unredeemable state—then a highly sensitive test may be preferred. Indeed, whether

either test is worth performing at all cannot be

determined by examination of its sensitivity and

specificity alone. One must know the implications of each kind of test result (true positive,

false positive, true negative, false negative) for

the health and well-being of the patient and for

the cost of medical care (54). Nevertheless, these

components of diagnostic efficiency must be

known if such analysis of the test’s implications

for outcomes is to take place. The problem with

studies using these efficiency measures is that

they often draw inferences about the usefulness

of one diagnostic strategy versus another without further analysis.

Summary indexes of diagnostic efficiency

have been developed by collapsing sensitivity

and specificity into composite measures. The

most common is diagnostic accuracy, * defined

as the proportion of all test results that are correct, and measured as the sum of true-positive

and true-negative results divided by the total

number of tests. This index of efficiency is attractive because it is comprehensible, but it is

more dangerous than the separate use of sensitivity and specificity because it assumes that the

two kinds of testing error (false positive and

false negatives) are equally important. This assumption is arbitrary and, for the vast majority

of diagnostic tests, invalid. By using it, the investigator has bought into the equal valuation of

the two kinds of error. Inferences, usually incorrect, are almost inevitable.

Diagnostic accuracy has also been criticized

because, unlike sensitivity and specificity, it systematically varies with the prevalence of disease

in the sample of patients under study. If the sensitivity of a test exceeds its specificity, then the

higher the prevalence of disease in the study

sample, the higher will be the measured diagnostic accuracy. This property is viewed as dangerous by some, for it implies that by manipulating the selection of patients under study, the investigator has the power to predetermine measured accuracy (41). However, the source of this

problem is not the measure itself but the inappropriate generalization of study findings to

populations not represented by the study sample. If one test proves more accurate than

another in a random sample of men over 65 who

*Semantic problems abound in the literature. Although accuracy is generally defined as above, the same measure is referred to

by at least one author as “validity” (41).
Ch. 2—Evaluation Models ● 11

are hospitalized for suspected lung disease, and

if there are no suspected sampling biases, * then

the test will also be more accurate in all such patients. In any event, this problem is minor compared to the assumptions of equal importance of

all kinds of error.

Another index of diagnostic efficiency is the

likelihood ratio, L, defined as the ratio of the

true-positive rate (sensitivity) to the false-positive rate (1 – specificity), or,

L = Sensitivity

1 – Specificity

Since sensitivity and specificity take on values

between O and 1, L must lie between O and 8. L

can also be interpreted as the rate at which the

odds in favor of disease prior to having test

results are translated into odds in favor of disease after the test results are known. * * Thus, it

is a measure of the information content of the

test, Very high or very low values of L imply

high information content, while a value of L

“hlost studies are based on patients at a single hospital or institution, The sample ma y be representative of those presenting at

the hospital, but there is always a problem in generalizing beyond

the particular institutions, for patient population~ vary widely

among hospitals.

‘ *The mathematical derivation of this interpretation is given by

McNeil and Mellins (81],

STUDIES OF DIAGNOSTIC YIELD

Diagnostic yield is defined as the proportion

of all test results found to be positive or abnormal. This measure of effectiveness is employed

in evaluating the usefulness of a diagnostic X-ray

procedure in a group of individuals with a specified set of signs, symptoms, or risk factors. Investigators typically compare yields of two or

more alternative diagnostic strategies, one involving the X-ray procedure, the other(s) not. If

the diagnostic yield of the strategy using the

X-ray procedure is low relative to competing

strategies, the inference is that the X-ray procedure is unjustified.

The concept of diagnostic yield is employed

most frequently in evaluating the usefulness of

near 1 implies that a test adds little information

to assist in diagnosis.

Unlike diagnostic accuracy, the likelihood

ratio does not vary with disease prevalence, but

it, too, makes implicit assumptions about the

relative importance of the different kinds of testing errors. L is essentially a measure of the ability of a test to remove uncertainty, but uncertainty of different kinds may be more or less

important to the patient. By collapsing sensitivity and specificity into a single composite index,

one loses the ingredients necessary for such an

analysis.

Other measures of diagnostic efficiency such

as the predictive value of a positive test (55) are

also available. They are essentially variations of

the indexes described here, and they also suffer

from the general limitations described above.

To summarize, measurement of the basic constituents of diagnostic efficiency—sensitivity

and specificity—is a critical first step in obtaining information necessary for decisions about

the use of a diagnostic test, but it is generally an

insufficient guide for decisionmaking unless

much is known or can be assumed about the importance of each kind of testing error. In any

case, the use of summary indexes of diagnostic

accuracy in the absence of reporting on sensitivity and specificity is inadequate.

an X-ray procedure as a screening tool. Here, the

study population is defined by demographic and

behavioral risk factors such as age, sex, occupation, history of smoking, or admission to a hospital. Symptoms or physical signs causing suspicion of a disease detectable by the X-ray a r e

absent. The X-ray procedure has potential for

detecting radiographic signs of occult (symptomatic) disease, presumably in early and mor e

manageable stages than would appear with

symptoms. The diagnostic strategies in contention are generally straightforward: screening V.

no screening. The diagnoslic yield of the screening procedure thus represents the net difference

in the number of cases detected between the

screening and no screening options.
12 Ž Background Paper #5: Four Common X-Ray Procedures: Problems and Prospects for Economic Evaluation

The cost of the screening program is often introduced as an element of the analysis. The casefinding cost (i.e., cost per abnormal) is estimated

as the unit cost of the procedure divided by diagnostic yield. High case-finding costs are generally interpreted as evidence against the use of an

X-ray procedure on the class of individuals in

question.

Just as measures of diagnostic efficiency give

inadequate consideration to the implications of

different kinds of errors, so too does diagnostic

yield. The negative finding, whether correct or

incorrect, appears to have no value. Yet, negative results may point the way to other possible

diagnosis and often reassure the patient, a function of considerable value in some situations

(51).

Diagnostic yield is also insensitive to the potential significance of positive findings. When

abnormalities detected by the X-ray are already

known or could have been detected by simpler

diagnostic approaches not considered, or when

knowledge of an abnormality does not affect

subsequent management of the case because it is

either clinically insignificant or not amenable to

STUDIES OF HIGH-YIELD CRITERIA

The “high-yield criteria” approach is an interesting variation on diagnostic yield. Whereas

studies of diagnostic yield attempt to identify the

best diagnostic strategy for individuals or patients with prespecified presenting conditions,

studies of high-yield criteria have as their objective the identification of the presenting conditions (signs, symptoms, risk factors, etc. ) that

would justify a diagnostic strategy (namely, the

use of the X-ray test). A diverse set of individuals is partitioned into two groups: those for

whom the diagnostic X-ray strategy is preferred

to other strategies, and those for whom the

X-ray strategy is inferior to other strategies. The

high-yield criteria are the factors used to partition the universe of patients.

This approach is most frequent in studies of

the use of X-ray procedures in symptomatic patients, where there are many combinations of

treatment, then the use of diagnostic yield as an

evaluative criterion overestimates the clinical

value of a test. Consequently, many researchers

use a modified definition of diagnostic yield,

counting as abnormal only those cases whose

test results are “important,” “clinically significant, ” or unknown prior to the test. This approach attempts to incorporate into the definition of “abnormal” some consideration of the

health and economic implications of the finding.

When is the diagnostic yield a useful evaluative endpoint? Three conditions must hold:

1) it must be reasonable to ignore the reassurance value of a negative finding, 2) a false-positive result should not imply costly or risky followup procedures, and 3) a true-positive result

should be likely to significantly influence

therapy and outcome. Under these conditions,

comparison of the diagnostic yield of alternative

tests or testing strategies will generally result in

appropriate medical decisions. Few diagnostic

testing alternatives meet all of these conditions.

To the extent that they do not, the results of

such analyses should be interpreted cautiously.

presenting signs and symptoms that are potential indications for the procedure. The analysis

proceeds on the assumption that if presenting

conditions can be identified which account for

the vast majority of positive findings, then the

diagnostic yield can be improved by limiting the

procedure only to patients with these conditions. The high-yield conditions so identified become X-ray referral criteria.

The performance of a set of high-yield criteria

must be assessed, but this cannot be accomplished by applying the new criteria to the sample of patients used to create them. Testing on

independent patient samples taken from the

same population is necessary, and performance,

as measured by the number of positives who

were missed and the number of X-rays saved,

will always deteriorate from the original data set

(86). Moreover, if the criteria are applied in pa-
Ch, 2—Evaluation Models ● 13

tient populations that are inherently different

from the sample used to create them, performance may increase or decrease markedly.

Virtually all high-yield criteria studies analyze

data on a sample of patients referred for the

X-ray procedure under study. The sample is

biased in that patients with the same presenting

conditions who are not referred for X-ray are

not included in the study. The result is probably

to overestimate diagnostic yield in patients with

moderate signs and symptoms.

as the relevant evaluative endpoint, The problems that plague diagnostic yield as a valid measure are equally germane to this discussion. How

can one logically choose among signs and symptoms to maximize the diagnostic yield of a test

when the implications of an abnormal finding

(or of a normal finding) are unknown or their

benefits doubtful? These limitations should be

kept in mind in assessing whether the decision

situation is appropriate to the application of this

technique.

The greatest weakness of studies of high-yield

criteria stems from their use of diagnostic yield

STUDIES OF DIAGNOSTIC INFORMATION

An alternative to the use of objectively measurable endpoints, such as sensitivity, specificity,

or diagnostic yield, is to measure the impact of

the test on the probabilities that physicians subjectively assign to possible diagnoses. If a test

finding, positive or negative, has very little impact on such subjective probabilities, then it

may be assumed that it has little impact on therapy and outcomes. The information value of the

test, then, is measured as the degree of change in

physicians’ subjective probabilities brought

about by the performance of the test.

The information value of the test is attractive

as an evaluative measure because it makes a connection, admittedly loose, with therapy and outcomes, and because it considers both positive

and negative test findings as important. But the

use of physicians’ subjective probabilities as the

basis for measuring information content is troublesome. Since the likelihood ratio, discussed

above, is a completely analogous measure of information content based on objective measures

(sensitivity and specificity), it is questionable

why one would wish to introduce into an evaluation of a diagnostic strategy the inaccuracy inherent in subjective probability assessments by

physicians.

The design of a study to assess the information content of a test is difficult at best. Contrived clinical situations would be needed to protect against biased posttest probability assessments by physicians who had committed themselves to ordering the test. Though the design of

studies of test sensitivity and specificity is also

difficult for interpretive tests such as X-rays, the

introduction of respondent bias is an unnecessary complication.

This approach assumes that the alternative

strategy to the test is a state of zero information.

The information content Of the test is measured

at two points in time: once before and once after

its performance. The change in probabilities between these times is attributed wholly to the test

results. The assumption is that probabilities

would not have changed over time in the absence of the X-ray, or that if more time were

allowed to elapse, more information would not

be forthcoming as the clinical course progressed.

The more appropriate comparison would be between the information available immediately

from the X-ray and the information that would

be obtained in time as further clinical information emerges. This tradeoff between early and

late information can only be compared by looking at the implications of a delay in therapy for

patient outcomes and costs.

It is difficult to imagine how the information

content of a test could be used to influence medical decisions. Supppose one found that over

half of the procedures performed added little information. Would that imply that the procedure

is being wasted? Not necessarily, for if the cost
14 • Background Paper #5: Four Common X-Ray Procedures: Problems and Prospects for Economic Evaluation

of missing a rare disease is high (that is, if lives test in this way would insure that a substantial

are lost), then one might be willing to use a test proportion of cases would have similar pretest

to rule out the disease, depending on the dollar and posttest probabilities and, hence, index

costs and medical risks of the test. But using a values close to zero.

STUDIES OF OUTCOMES

The inadequacies of diagnostic endpoints can

be overcome only by research into the implications of test findings for patient outcomes, including mortality, morbidity, and quality of life.

A few studies have attempted to relate the findings from diagnostic X-rays to ultimate outcomes of the medical process. Outcome measures such as 1- or 5-year survival rates and years

of life saved have been applied in a few studies.

Alternative diagnostic strategies are compared

for their ultimate impact on health outcomes

and sometimes on the cost of achieving those

outcomes.

Studies of this kind require that either a great

deal of evidence be available in the literature on

the outcome of alternative therapies or expensive prospective and well-controlled studies will

be performed to obtain outcome data. Given

these requirements, it is understandable that few

studies fall into this category.
.

3 .

Chest X-Ray
UTILIZATION, COSTS, AND CONTROVERSIES

In 1970, approximately 48 million radiographic X-ray examinations of the chest were

performed, accounting for almost one-half of

the total volume of X-ray examinations in the

United States. About 64 percent of these chest

X-ra y examinations were performed in hospitals; the rest were performed in private offices or

groups, or in health agencies (31). Though there

are no available data listing indications for chest

X-rays in various settings, the common practice

of routine chest X-ray on admission to hospitals

or prior to surgery is likely to contribute

substantially to the use of chest X-ray, (In 1977,

there were approximately 34 million admissions

to short-term hospitals in the United States. ) In

many hospital emergency rooms and outpatient

departments, chest X-rays are performed routinely if a complaint refers to the chest in any

way (10,76),

Although the volume of procedures is high,

chest X-rays accounted for less than one-third of

the total films used in 1970, owing to a belowaverage number of films per examination. The

mean number of films used per chest examination was 1.7, whereas the average for all body

areas is 2.4 films per examination. As with all

procedures using ionizing radiation, the chest

X-ray subjects the patient to radiation exposure.

The biological effect of radiation is expressed

in “rads,” i.e., the amount of energy absorbed at

particular points in the body, such as the bone

marrow, thyroid, and gonads. All of these

points are associated with different effects, such

as leukemia, malignant tumors, possible impairment of fertility, or genetic effects (28). The median gonad dose to males and females from diagnostic chest radiographs is very small, less than

0.5 millirad per exam. Photofluorographic chest

exams to females have a median gonadal dose of

1 millirad per exam, also a low dosage, The bone

marrow dose produced by chest radiographs is

relatively low too, at about 10 millirads per

exam (28). The radiation exposure on each chest

film is also relatively low. On average, the radiograph exposed the patient to 47 millirads

compared to an average exposure of 310 millirads for skull films and 70 millirads for forearm

films. Thus, although the volume of chest examinations is high relative to other X-ray procedures, the total dose to which the population

was exposed represented a much lower proportion of the total dose exposure from all medical

X-rays.

Chest X-rays are also inexpensive relative to

other diagnostic X-ray procedures. In a 1975

sample of physician charges for X-ray procedures in California, the average bill for a twoview chest X-ray was $25.15, compared, for example, to $47.40 for a complete skull examination (121).

Information on the setting in which chest

X-rays are performed is scanty, but some limited

evidence based on California medicaid claims

data is available. All medicaid claims submitted

by physicians in the first quarter of 1978 were

compiled for specific chest X-ray procedures.

The claims indicate the location of service and

specialty of the physician performing the service. Tables 3 and 4 show the distribution of chest

X-ray claims submitted by physicians and radiologists in California, Although these data do

not include all such procedures performed (i. e,

X-ray procedures performed in hospitals which

bill directly for both technical and professional

charges are not included), they do show the relative importance of simple v. more complicated

chest X-ray procedures. Notice that two-view

chest X-rays are much more common reIative to

single-view examinations in the ambulatory care

setting than in the inpatient setting (table 3).

This may result from the frequent use of portable X-ray equipment on critically ill patients in

hospitals where it is technically infeasible to obtain more than one view.

17
18 ● Background paper #5: Four Common X-Ray Procedures: Problems and Prospects for Economic Evaluation

Table 3.—Medicaid Chest X-Ray Claims in California Submitted by Physicians in First Quarter

of 1978, by Location of Service

Inpatient a Outpatient a Office Other Total

71010 Chest: single view. . . . . . . . . . 12,605 (38.4°/0) 3,183 (1 2.4%) 13,230 (12,1 0/~) 3,456 (22.900/. )

71020 Chest: two views. . . . . . . . . . . 19,753 (60.20/.) 22,295 (86.6%) 95,037 (86.90/.) 11,639 (77.10°/0)

71021 Chest: three views. . . . . . . . . . 207 (00.6%) 129 (00.5°/0) 262 (00.2%) 2 (00.01%)

71030 Chest: complete (minimum

of four views). . . . . . . . . . . . . 255 (00.8°/0) 123 (00.5°/0) 789 (00.7°/0) —

Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32,820 25,730 109,318 15,097

32,474 (17.8%)

148,724 (81 .7°/0)

600 (00.3%)

151 (00.1 0/0)

181,949

aRecorded only when hospital and physlclan bill separately for the serv[ce (split blll!ng arrangement)

SOURCE Urban Inst!tute sample of 5,000 solo practltloners, Includtng 177 radiologists

Table 4.—Medicaid Chest X-Ray Claims in California Submitted by Radiologists in First Quarter

of 1978, by Location of Service

Inpatient a Out patienta Office Other Total

71010 Chest: single view. . . . . . . . . . . . 11,836 (39.5°/0) 3,127 (12.4°/0) 1,371 (04.20/o) 34 (03.70%) 16,503 (18.30/o)

71020 Chest: two views. . . . . . . . . 17,695 (59.O%) 21,944 (86.7%) 31,005 (94.4°/0) 878 (95.00°/0) 72,594 (80.4%)

71021 Chest: three views. . . . . . ., . 204 (00.7%) 126 (00.5%) 168 (00.5%) 1 (00.01 0

/0) 499 (00.6%)

71030 Chest: complete (minimum

of four views). . . . . . 249 (00.8°/0) 121 (00.50/0) 288 (00.970) 11 (01.2070) 675 (00.7°/0)

Total . . . . . . . . . . . . ... ... . . . . 29,984 25,318 32,832 — 924 90,271

ar+eCorded only when fl~~pltal and pflyslclan bill separately for the service (sPllt blllln9 arrangement)

SOURCE Urban Institute sample of 177 solo radiologists (326 percent of solo radiologists In Call fornla)

Virtually all medicaid chest X-ray examinations in California hospitals in 1978 were performed by radiologists. Other kinds of physicians played a more important role in performing chest X-rays in physicians’ offices. About 70

percent of all medicaid chest X-rays in physicians’ offices were performed by nonradiologists.

As expected, radiologists tend to perform

more intensive chest X-ray examinations than do

other kinds of physicians. Only 4 percent of

chest X-rays performed by radiologists in their

offices were for single-film examinations, while

15 percent of chest X-rays performed by other

physicians were single-film procedures.

The high volume of chest X-ray procedures is

due in large part to its importance as a screening

test. Chest X-rays have been used to screen for

cardiopulmonary disease in the general population and in selected high-risk groups. They have

also been advocated for use in healthly populations as a baseline measure for evaluation of

future radiographs (14,42). Chest X-ray screening has most frequently been advocated for detection of tuberculosis (TB), lung cancer, and

cardiovascular disease. Its use has been encouraged by hospital and nursing home policies

which have dictated routine admission or preoperative chest radiographs, by laws or regulations

which have required chest X-rays of workers in

high-risk occupations, by colleges and summer

camps which have required prematriculation

chest X-rays, and by public health agencies

which have made chest X-ray examinations

available to selected high-risk groups and sometimes to the public at large. These screening uses

have had pervasive effects on the American public. Over 80 percent of all noninstitutionalized

Americans over 17 years of age in 1973 had had

at least one chest X-ray procedure. Thirty-one

percent had received the examination in the previous year (29). There is no source of data, recent or old, on the proportion of chest X-ray examinations performed for screening purposes.

However, the Bureau of Radiological Health

reported that in 1.970, about 20 percent of all radiologic examinations of the thorax were conducted at health agencies. * It may be assumed

*About 9 percent of these chest X-ray examinations were photofluorograms, a procedure whose appropriateness relative to the radiograph has been questioned (31).
Ch. 3—Chest X-Ray Ž 19

that the vast majority of these examinations

were performed for screening purposes. Since a

large but unknown proportion of the chest

X-rays performed at other locations such as hospitals and physicians’ offices are also for screening purposes, the contribution of screening to

total chest X-ray volume in 1970 is likely to have

been well above 20 percent.

The popularity of chest X-ray as a screening

procedure has declined in the past decade, partly

in response to the secular decline in the prevalence of TB, one major target of chest X-ray

screening programs (102, 115). The change in attitudes about the appropriate place of chest

X-rays is also a result of the myriad research

studies documenting low diagnostic yield and

high case-finding costs of many chest X-ray

screening programs, even those targeted at highrisk groups. In the 1970’s, public and quasi-public bodies issued recommendations reversing

policies toward chest X-ray screening programs;

these recommendations have rested on the studies of diagnostic yield in various populations

(27,94), Today, the literature on chest X-ray

screening for TB appears to be focused on workers in foodhandling occupations (18,108) and on

high-prevalence groups, such as refugees from

Southeast Asia, where a very high proportion

would be expected to react positively to the tuberculin skin test due to high levels of exposure

to the tuberclin bacillus (31,67). Nevertheless,

selective screening programs using chest X-rays

still exist. For example, all immigrants are required to have chest X-rays, and in many States,

teachers’, hairdressers’, nurses’, and other health

professionals’ X-ray screening programs continue. Currently, there is much debate over

whether the X-ray should be used to screen highrisk groups for lung cancer (4,44).

Although most of the controversy over the

chest X-ray examination has centered on its use

CHEST X-RAY EVALUATIONS

This section summarizes the most prominent

evaluation studies of the chest X-ray in the last

on asymptomatic people, there has been some

concern about the use of chest X-ray in diagnostic contexts. In particular, the frequency of

radiographic followup of patients with cardiopulmonary disease has been raised as an issue in

the evaluative literature. How often, for example, should a patient hospitalized for pneumonia

be subjected to a chest X-ray, both during the

hospital stay and after discharge? Hospital

polic y or medical practice may dictate too frequent followup examinations, * thus subjecting

the patient to unnecessary radiation and medical

costs.

There is also substantial question about appropriate radiological methods, Some of these

issues are the number of views (hence, films)

needed, the appropriateness of photofluorography radiography, the necessary level of expertise or credentials of the reader, and the optimal number of readers. Clinical studies have

compared the additional diagnostic yield obtained from the two-view chest examination

with that obtained from the single-view procedure (105). Other studies have assessed the

diagnostic efficiency of alternative reader and

equipment configurations (60).

Aside from these questions of appropriate radiological method, evaluation of the usefulness

of the chest X-ray in symptomatic patients has

been limited. TO our knowledge, there have

been no attempts to evaluate diagnostic efficiency or outcomes of chest X-rays in patients with

particular kinds of signs or symptoms; only one

study of high-yield criteria for ordering chest

films has been attempted to date (10).

*It IS possible that medical practices dictate too tew IoIIowuP examlnatl<~n~ and thereby subject the patient t~~ p<>[~rer expecte d

health ,}utcomes. Problems in the directit~n ot t[~(~ few radiographs

do n~~t appear to hold much attention in the Ii tera t u re.

10 years, The purpose of this review is not only

to document the evidence available to support
20 • Background Paper #5: Four Common X-Ray Procedures: Problems and Prospects for Economic Evaluation

decisions about the use of chest X-rays, but also

to identify and assess the importance of methodological problems inherent in the literature.

The review is organized into these general categories: 1) studies of chest X-ray as a screening

device, 2) studies of diagnostic uses of chest

X-ray, and 3) studies of radiological method. Because the screening literature is large, it has been

further divided into studies of community-based

chest X-ray screening for TB, community-based

screening for lung cancer, and X-ray screening

for cardiopulmonary problems in selected patient populations.

Studies of Community-Based

TB Screening Programs

The use of the chest X-ray as a mass screening

tool for the detection of tuberculosis was common in public health departments in the 1940’s

and 1950’s. As information accumulated on the

low diagnostic yield of chest X-rays, however,

the cost effectiveness of these programs was increasingly questioned (62,73,113). Table 5 summarizes the findings of studies published in the

early 1970’s on the usefulness of chest X-ray

screening for TB. Virtually all of these studies

used diagnostic yield as the principal evaluative

criterion. The diagnostic yield of TB cases is

calculated from a series of chest X-rays on large

numbers of individuals. In those with neither

symptoms nor high-risk factors such as alcohol

abuse, the TB yield was found to be universally

below 0.5 percent. Targeting screening programs to high-risk locales did not raise the yield.

The observed diagnostic yield of a test varies

directly with the prevalence of the disease in the

population studied. As disease prevalence decreases, diagnostic yield will decrease and casefinding costs will rise. After definitive antibiotic

therapy for TB became available in the United

States, the mass chest X-ray programs experienced rapidly decreasing yields.

The use of diagnostic yield or case-finding

cost as a criterion for evaluating a screening program requires an implicit assumption about the

implications of finding a case. If, for example, it

is concluded that a screening program with a

diagnostic yield of 1 percent is unjustified, one

must assume that the benefits to the 1 percent of

cases found do not outweigh the cost of the

screening program. In the case of TB screening,

the rarely expressed assumption is that TB discovered in its early symptomatic stages is curable and that the risks of disease communication

by undetected active cases do not warrant the

cost and radiological risk of the screening proTable 5.—Screening for Tuberculosis

Study a

Lewis (73)

Swallow and

Sbarbaro (113)

Retchman (102)

Felngold (39)

Horwttz and

Darrow (62)

Year(s) of data Population

collection description

1969 Ghetto population

1965-70 General urban

population (Denver)

1970 General urban

population (New

York City)

1972-75 Primarily elderly

and chronically Ill

outpatients

1972 Danish adults

Number

of cases Sample

109,000 Cleveland mobile

X-ray mass screening

program for TB

— All TB screening and

case- finding pro.

grams in Denver for

5 years are retro.

spectively analyzed

283,000 –

TB yield

0.01%

a) Detected O 010, of new

active disease

b) Inactive TB detected in

O.3% of people X-rayed

c) Other abnormal conditions

found at rate of 3 3° ,

0 02”,

48,000 Over 3 years, cases 0.05%

taken from the

general medical out

patient Clinic of an

urban hospital

677,800 Those appearing in o 02” 0

Danish chest clinic

for mass screening

Case-finding

cost Comments

This O .01% was 5% of

the new cases

reported that year

$8,115 Only 13.5% of new

active cases iS found

$ 372 by screening

$ 35

$4091 50% of the new cases

were in alcohol

abusers

Symptomatic patients

examined by chest

X ray in same clinic

had TB yield of O 3° ,

aNumbers In parentheses refer to references (n the Itst that appears at the end of thts background paper
Ch. 3—Chest X-Ray • 21

gram. If TB were incurable once it reached the

clinical stage but completely curable in the preclinical stage, a different consensus might be

reached about the minimum level of diagnostic

yield required to justify a screening program,

The reliance on diagnostic yield as a criterion

for evaluating chest X-ray screening programs is

curious, especially in light of the exampIes of

good outcome-oriented evaluations of other

screening and preventive technologies that are

available in the literature (23,96,109). The development of a cost-benefit evacuative framework

for analyzing the value of chest X-ray screening

programs in populations with varying TB prevalence rates would be useful in resolving issues

that are likely to continue to arise as new highrisk groups are identified.

Public health agencies and professional societies and associations have been influenced by

the studies of diagnostic yield. In 1972, the Department of Health, Education, and Welfare

issued a policy statement recommending against

chest X-ray screening programs in the general

population and in favor of limiting its use as a

screening tool to adults in selected high prevalence populations. In other groups, the chest

X-ray would be a followup procedure to positive

reactions on tuberculin skin tests (27). This

statement superseded a department policy dating back to 1958, which endorsed communitybased chest X-ray screening programs, particularly when targeted to high-risk groups.

Prior to the 1972 statement, the National Tuberculosis and Respiratory Disease Association, the

American College of Chest Physicians, and the

American College of Radiology had issued similar statements against mass chest X-ray screening programs.

Lung Cancer Screening

The question of whether periodic chest X-ray

screening for lung cancer is useful in high-risk

groups (generally comprising smokers over 40

years of age) has been analyzed by evaluative

criteria that differ markedly from those used to

analyze TB screening. Research on lung cancer

screening has gone beyond calculation of diagnostic yield to consider the net effect of periodic

screening on 2-, 3-, and 5-year survival rates and

in some cases mortality rates from lung cancer,

This emphasis on final outcomes of the disease

process results from the lack of a viable therapy

for almost all but the earliest localized lung

cancers. For these, resection (removal) of the

diseased lung offers the only hope of cure. To be

effective, then, a screening strategy must be able

to detect cancers while they are still locaIized.

To the extent that periodic screening does, indeed, uncover localized lung cancers, it is a lifesaving measure, At present, however, the evacuation and staging of lung cancers is imprecise,

and the ultimate proof of cure comes only with

time. Thus, diagnostic yield, or even the yield of

apparently respectable cancers, is inadequate.

Most investigators have compared 5-year lung

cancer survival rates in screened and unscreened

populations,

Lung cancer screening programs vary in their

particulars, The testing protocols of some programs have involved a chest X-ray only, while

others have included sputum. The frequency of

screening has also varied. Annual, semiannual,

and even more frequent examinations have been

offered to participants,

Table 6 summarizes the results of the principal

studies of lung cancer screening in the past 15

years. Randomized lung cancer screening studies

are ongoing in three institutions— the Mayo

Clinic, Memorial Sloan Kettering, and The

Johns Hopkins University–as part of an evaluation of lung cancer detection methods sponsored

by the National Cancer Institute (see table 6).

The final results of these studies are not yet

available.

The studies of lung cancer screening presented

in table 6 are difficult to compare because of the

different time periods covered, screening protocols undertaken, and biases inherent in their

design. Most studies have not been randomized,

leaving open the possibility that participant selfselection may have distorted the results. It is also

difficult to interpret the 2- or 5-year survival rate

when survival is counted from the time of disease detection. Screened groups may be expected

to have higher survival rates simply because

their disease is detected earlier, independent of

the effect of surgery. Although the measured
22 ● Background Paper #5: Four Common X-Ray Procedures: Problems and Prospects for Economic Evaluation

Table 6.—Screening for Lung Cancer

Year(s) of data Patient Number Patient

of cases sample selection

Screening cost

per cure

$83,000

Outcome/overall

mortality

80/0 of detected cases

survived 5 years

Study a

collection Yield

2%

(excluding results

of Initial tests)

description

Men, 45 years and

older

Boucot (15)-

1951-61 6,136

13,000

29,723

2,112

14,607

10,362-

11,000 

6,612

10,713

Prospective study of

asymptomatic male

volunteers in biannual

screening over 1O-year

period.

Prospective study of

asymptomatic adults in

routine annual screening

program at University

Medical Center

Over 3 years.

Gilbertsen and

Lillehei (50}

1950-69 0 080/0 — 10% of detected cases

had 5-year survival

Adults, 45 years

and older

Brett (16) 1965-68 Men, 40 years and

older, in British

factories

0.3%

(excluding results

of Initial tests)

15% had a 5-year survival rate Test group was given

semiannual X-rays

Control group radio.

graphed at beginning and

end of study

Screening in Vancouver

by X-ray and sputum

cytology

O.3%

(excluding results

of Initial tests)

o. 47%

(found by X-ray)

6% had a 5-year survival rate

Gryzbowski

and Coy (53)

Men-over 40,

smokers, and one

additional risk

factor

Residents of

Veterans Adminis.

tration Domicil.

iaries, who were

at high risk of

developing lung

cancer

1969 —

Lilienfeld (74) 1958-61 Residents were screened

approximately every 6

months for 3 years, by

chest X-ray and/or

sputum cytology

0.01% $1.000 for-a workup

on a SUSPICIOUS

X-ray

12% 3-year survival rate

in respectable cases.

13°/0 of the diagnosed

cases were respectable

Borrie (14) 1976 Tokyo Health Control

Center

One year

11 per 100,000 (o 01 %)

for patients over

60 105 per 100,000

(1%)

1.1‘/. “suspected

cancer.

0.3% confirmed

cancer (results of

lnitial screening)

Stitik and

Tockman (1 12)

1973-78 Men, ever 6 5

years old, smoke

a pack of

cigarettes per day

or more

‘Randomized clinical trial,

volunteers selected from

Maryland records Control

group IS given annual

chest X-rays (4 views).

Study group IS given annual chest X-rays and

sputum cytology every 4

months

Randomized clinical

trial—control group is offered an annual chest

X-ray.

Fontana (43)

(and as

reported by

American

Cancer

Society)

Men, 45 years and

older, who

smoked one or

more packs of

cigarettes a day

1971-76 — —

Study group IS screened

with sputum cytology and

chest X-rays every 4

months

Randomized clinical

trial—control group 3,387

men given annual chest

X-ray

O.03% early —

cancer

Melamed,

et al (88)

1971-76 Men, over 40

cigarette smokers,

at a high risk

Study group 3,325 men

given annual chest X-ray

and sputum cytology

every 4 months

Study group of 5,156

0.03% early

cancer found by

X ray

Dales,

et al (22)

1964-75 Men and women Savings of over Death rate per 1,000 for

$2,100 per study 11 year study period

group, men 45 to 54 due to cancer of bron

years of age No chus and lung,

—

aged 35 to 54 at

beginning of

study, residents of

San Francisco

Bay Area and

members for > 2

years of Kaiser

Foundation

Health Plan

members urged to take

annual multiphasic health

checkups (including

chest X-ray)

Control group of 5,557

members not so urged

net savings

associated with Control 47

younger men or Study 49

women

aNumbers ,n parentheses refer to references In the Ilst that appear at the end of this background PaPer
Ch. 3—Chest X-Ray . 23

survival rates can be corrected for this “leadtime

bias” (125), the lung cancer mortality rate is a

more appropriate outcome measure. The ongoing randomized studies are expected to measure

the impact of their screening protocols on lung

cancer mortality.

Recognizing these limitations, the findings to

date do not support the notion that X-ray

screening programs have a favorable impact on

lung cancer survival. In a recent study of the

issue, the American Cancer Society (ACS)

reached the same conclusion (4). In addition to

the results reported in table 6, the authors of that

study had access to some preliminary results of

the Mayo Clinic lung cancer study which

showed no difference in mortality rates between

screened and unscreened populations. The ACS

study emphasized the long and costly search for

cancer sometimes initiated by cost, morbidity,

and time needed to localize a tumor when the

sputum cytology is positive or suspicious and

the chest X-ray is negative. In the absence of evidence suggesting beneficial effects on mortality,

these problems of followup and the cost of

screening led ACS to recommend against periodic screening.

The ACS action has been controversial. The

principal investigators of the Mayo Clinic study

have argued that the recommendation was premature because it used preliminary results (44),

More recent data may indeed show improvement in mortality rates (90), Moreover, according to the investigators in the lung cancer detection study, the need for long and costly followup

is a relatively rare event. *

While all parties to the debate agree that mass

lung cancer screening programs are not justified

by the evidence available at this time, there is

sharp disagreement as to how the physician

should advise the individual patient seeking a

physical examination. The ACS board believes

that physicians should discourage periodic lung

cancer detection procedures, because their benefits have not been demonstrated, while their

costs are high. Other-s believe that since screen-

*It 1~ cstim-ateci b} I{tlbcrt Fontana Nl, L),, of the hlayo Clinic,

that {~nl} IS percent ot pc~sitive \putum finding~ are accompanied

b} ne~at]k[’ chest X-ra\\ (per~ona] c [}mmunication ).

ing is the only possibility for detecting lung cancer early, cost should not be considered in the individual decision (44).

To some extent, the issue can be resolved by

considering who pays for the screening examination. If the patient is fully and fairly informed

about the evidence on benefits and risks and is

prepared to pay for the procedure out-ofpocket, then by definition the procedure is

worth its costs to that patient. If, however, the

screening test is covered by third-party payers

such as public or private insurers, the issue of

physician responsibility is, or at least should be,

more complex. Since the patient is subsidized,

the patient may demand a test for which he or

she would not otherwise be willing to pay. TO

the extent that the ACS interpretation of the

benefits, risks, and costs of lung cancer screening is accurate, promulgation of this information

and its recommendations is a valuable service to

both patients and third-party payers.

Studies of Chest X-Ray Screening of

Selected Patient Populations

The use of chest X-ray as a routine screening

test for cardiopulmonary abnormalities in patients with unrelated complaints has been

studied many times. Table 7 presents summaries

of the most important studes. Diagnostic yield

and case-finding cost appear to be the most

widely used criteria for evaluating these uses of

the chest X-ray, but many studies differentiate

between the total yield and the yield of clinically

significant findings.

In studies of routine hospital admission and

preoperative X-rays, the diagnostic yield differed widely with age of patient (105), but, even

within particular age groups, the variation in

diagnostic yield from study to study is high. For

example, one study of admission chest X-ray

yield from study to study is high. For example,

one study of admission chest X-ray yield in a

geriatric hospital reported 2 percent abnormalities (56), while another detected abnormalities in

16 percent of patients over 40 years of age (105).

Such variation may be due to differences in patient case mix, reader definition of abnormality,

radiological method, or reader competence.
24 ● Background Paper #5: Four Common X-Ray Procedures: Problems and Prospects for Economic Evaluation

Table 7.—Chest X-Rays for Selected Patient Populations

Population

Other measures of efficacy

effectiveness

Yield

(as a percent

of N)

Year(s) of data

collection

1972

October 1973

to March 1974

Number

of cases

39,017

10,597

a) 6,063

521

3,689

b) 1,996

C) 2,538

36,475

102

195

44,663

1,500

1,000

350

10,619

1,000

Patient sample

selection

Cas e

finding cost

Effect on patient

management Comments

Effect not measured —

Four surgical cases

were postponed but

Study a

Feingold (39)

Sagel.

et al (105)

description

Routine hospital admission chest X-rayHospital admissions for the year2 cases (insignificant

percentage)

Hospital admis

sions and

preoperative pa

tients

Prospective study

of chest X-ray

taken over a

6-month period, in

three categories,

a) Routine

under 20 years

over 40 years

b) Possible chest

abnormality

c) Suspected

chest abnor

mantles

(For serious”

abnormalities)

the effect ‘on the

jority of cases IS

unknown

ma

a) 16%

0“ o

26° O

b) 34° o

C) 69%

Hammar (56) 1954-69 Delayed surgery (in

0.04%

Hospital admissions in a predominantly geriatric

hospital population

A retrospective

review of hospital

admission records

at a Minnesota

hospital

2% abnormalities detected

O 08°, new cases

TB

Bartha and

Nugent (8)

1974 Adults with

hypertension

All patients entering clinic over a

year’s time with

hypertension and

having a roentgenogram

24% $106

(estimated

at $25 per

examination)

No Influence on

hypertension

management

Steel, 1974

et al (111)

Gertatric patients Seen in clinic for

placement and

evaluation

Abnormalities of

aorta 11 20/0

Of heart and

lungs 61%

—

Pollen, et al 1969

(20)

Members of a San

Francisco health

maintenance

organization

These multiphasic

examinations

were performed

during a 12 month

period

7.4% $ 6.20b

under 40

21 “o,

over 60

19 2“o

— b

$21.90

$2.40

$316 per

Significant

finding (estimated at $15

per examina

tion}

November

1974 to June

1975.

A prospective

study Of 1,500

consecutive pre

operative children

Children (to 19

years), preoperative

7 4°, with abnormalities: 4.7% unsuspected significant abnormalities

3 8°. postponed or –

changed surgical

strategy

Sane,

et al (106)

Brill, —

et al (17)

Consecutive inpatients and outpatients in pediatric

clinic as part of

screening program—excludes

patients with positive TB tests or

known chest abnormal {ties

Routine preoperative chest roentgenograms reviewed retrospectively

Chosen chronologically, they ex

eluded cases of

thoracic surgery,

chest disorders

and major trauma

6%: 4% were

minor skeletal

abnormalities

No medical or

surgical treatment

rendered

Children up to 18

years old in low

income area

—

Farnsworth, – Children 15 months

et al (38) to 14 years, entering elective surgery

880,0 Surgery never —

cancel led, preoperative diagnosis never

changed

Royal College 1977 Patients in

of Radiologists (103)

8 British hospitals

participated in the

prospective study

of chest X-ray

Over a 2 month

period, preoperative patients

NA No effect on patient —

nonacute, management

noncardiopulmonary surgery

Loder (75) 1977 British inpatients. Over 30 Frequent changes in —

management of older

patients

—

11. 5%

Under 30

1 .14%
Ch. 3—Chest X-Ray Ž 25

Table 7.—Chest X-Rays for Selected Patient Populations—Continued

Other measures of efficacy

effectiveness

Yield

Year(s) of data Population Number Patient sample (as a percent Case Effect on patient

Study a

collection description of cases selection of N) finding cost management

Petterson and 1976 Middle class 1 530 All preoperative — $15,000 per Postponed surgery in

Janouver (98) hospital population patients postponed 2 cases

surgery

Rees, 1976 Preoperative paet al. (101) tients electing non

cardiopuImonary

surgery in males

Bone brake 1966-75 Pregnant women

et al. (1 1 ) given prenatal

chest roentgenograms

Mattox (87) 1972 Pregnant women

given prenatal

chest X ray

Schneider 1977 Sample of job can

and Dykan didates in New York

( 108) City hospital

Brubaker (18) 1971 Job applicants in

food manufacturing

plants were given

routine physicals

aNumbers ,n parentheses refer to references n the Itst

bcost of X.ray examination dld not Include overhead

667 Radiography per

formed on consecutive preoperative

noncardiopulmonary surgery

11,725 Retrospective

review of all available delivery

records at Mayo

Clinic

1,239 Retrospective

review of patient

records at Unversity Medical

Center

<30 years of age

number appreciable abnormality

O .6%

1 3°, (significant

abnormal find

ings)

3500 Chest X-rays were O

given to 14% of

this sample—

those over 40 with

a positive TB skin

test

29 During the year 14°, (4 findings

842 applicants out of 29 examiwere given physi - nations)

cat examinations

29 chest X rays

resulted

that appears at the end of this background paper

Frequently, the studies of chest X-rays in hospital medical or surgical inpatients have reported

on the proportion of cases in which the chest

X-ray changed patient management. With the

exception of two studies, one on chest X-rays in

children prior to surgery (106) and one on inpatients in a British hospital (7.5), the chest X-ray

appears to have negligible effects on plans for

surgery or other aspects of patient management.

A study by Sane, et al. (106) of preoperative

chest X-rays in children highlights the difficulty

of drawing conclusions for medical practice

from studies of diagnostic yield. In the study,

4.7 percent of all chest X-ray examinations

showed previously unsuspected, clinically

significant abnormalities. The cost of detecting

— —

$.2,773 No beneficial change

(estimated In patient manage

at $1750 per ment

examina -

tion)

$1,176 (ap –

proximately)

— —

$72

Comment s

—

38% had

chest X ray

in previous

year

—

All findings

would have

been discovered without

X rays except 1 be

nign nonin

fectious

case of T B —

case cost

approximateIy $20000 to

find

—

each abnormality was estimated at $316. * The

authors concluded that this “low” case-finding

cost justifies the use of the preoperative chest

X-ray. In a comment on the study, Neuhauser

laid out the kinds of information on subsequent

benefits and costs that would be needed to make

such a judgment with confidence (95). One

would need to know how the detection of abnormalities translates not only into changes in

patient management but also into ultimate patient outcomes. Even when the yield is so low as

to be negligible, the diagnostic yield alone is insufficient. For example, in a recent smaller study

of pediatric preoperative chest X-rays, only 1 of

● The cost of each chest X-ray examination was assumed to be

$15,

1
26 ● Background Paper #5: Four Common X-Ray Procedures: Problems and Prospects for Economic Evaluation

350 X-ray examinations revealed a clinically

consequential finding which could not have been

anticipated on the basis of the clinical history

and examination (38). To make sense of these results, one would need to know whether the clinically significant finding had an impact on mortality or morbidity,

In summary, the studies of chest X-ray screening in selected patient populations reveal wide

interinstitution variation in diagnostic yield for

similar types of patients and general use of an informative but incomplete evaluative measure—

the diagnostic yield—as the basis for inferences

about the appropriate place of chest X-ray in

medical practice. It is no wonder, then, that this

literature has had relatively little impact on routine X-ray policies of hospitals.

Studies of Patient Management

and Followup

How often should a patient with a cardiopulmonary disease be X-rayed for purposes of

monitoring patient progress? To our knowledge,

this question has been addressed only in the case

of tuberculosis and pneumonia.

The issue for tuberculosis has been framed in

terms of the need for periodic radiographic and

sputum examination in TB patients who have

completed a program of modern chemotherapy.

The diagnostic yield of TB on recalled patients

was found to be negligible in three studies

(2,6,33), leading the Center for Disease Control

and the American Thoracic Society in 1974 to

recommend against such a policy (5,25).

The annual number of hospital discharges for

pneumococcal pnemonia in the United States

has been estimated at approximately 382,000

(31). If all such pneumonia patients were

X-rayed one more time than is necessary over

the course of the disease, 382,000 unneeded

X-ray examinations would be conducted. Thus,

the question of optimal frequency of X-ray followup has major cost implications.

Jay and his colleagues prospectively followed

80 consecutive patients admitted to a teaching

hospital for acute bacterial pneumonia (65).

Typically, these patients were subjected to chest

X-ray examinations every 1 to 3 days in the hospital and every 2 weeks after discharge until radiographic abnormalities disappeared. In the 72

surviving patients, the standard radiographic

signs of pneumonia had disappeared in all patients by the eighth week from admission, but

after 4 weeks, 36 percent of radiographs were

still positive for pneumonia, At 4 weeks, almost

50 percent of the radiographs showed some form

of abnormality related to pneumonia, thus necessitating continued followup. The authors

concluded that the appropriate interval for radiographic followup after diagnosis is once at

the time of discharge from the hospital and subsequently at 6-week intervals.

A more recent study of radiographic followup

of pneumonia in children up to 15 years of age

showed that after 4 weeks 80 percent of the radiographs were normal, whereas complete resolution of radiographic findings occurred in all

patients after 6 weeks. These authors also concluded that in the absence of persistent signs or

symptoms, the interval between radiographs

should be 6 weeks (52).

Studies of changes in diagnostic yield over

time in followup examinations are productive in

identifying areas where significant savings can

occur. But as in other contexts, diagnostic yield

must be interpreted cautiously. In the instance of

pneumonia, evidence from the chest X-ray is not

generally used to alter therapy except when

symptoms persist over a long period of time. In

other conditions, the chest X-ray may be critical

for therapeutic decisions, and changes in the radiograph, while occurring in few patients, may

be important signals for therapeutic strategy.

Thus, in any study of chest X-ray as a followup

test, the implications of normal or abnormal

findings for therapy and outcomes must be understood and accounted for.

Studies of the Diagnostic Uses of

Chest X= Ray

Under the auspices of the American College of

Radiology, Lusted conducted a study of the information content of chest roentgenograms (and

other X-ray procedures) in hospital emergency

rooms (76). Information content was measured
Ch. 3—Chest X-Ray ● 2 7

-. —

by an index of the change in physicians’ assessments of the probability of disease due to the

chest X-ray. A large change in these subjective

probability estimates would mean that the X-ray

provided valuable diagnostic information.

While the value of such information can only be

assessed in terms of its impact on therapy and

outcomes, its existence is a necessary condition

for these ultimate results.

Before each chest X-ray procedure was performed, the ordering physician was asked to estimate the probability of the most significant disease and the most likely condition. After the

physician had reviewed the chest X-ray, these

probabilities were estimated again. Using a logarithmic index, the authors concluded that in

about 90 percent of all chest examinations, these

probabilities changed sufficiently to infer high

information content. *

The study contained some serious design

flaws. The selection of participating institutions

and physicians was not random and may well

have been seriously biased. When the ordering

physician was asked to revise his initial probability estimates after the X-ray, he was reminded of his early assessment, thus probably

strengthening an already existing bias toward

large changes in probability assessments. The index of probability change used in the study is

also difficult to interpret in terms of real gains in

information.

Even with these problems corrected, the findings of the study would offer little in the way of

information on the appropriate uses of chest

X-rays in emergency rooms, because the results

are aggregated across all presenting signs and

symptoms. Whether chest X-rays overall provide much or little information is of no consequence, for the information content most likely

varies widely among different kinds of patients

seen in emergency rooms. The objective of evaluation is to discover which indications are justified and which are not.

This objective has been pursued in a recent

study of symptomatic patients receiving chest

X-rays in an emergency room (10). Over 1,100

‘Tht’ c (~mput(d Inci(w ()} In! L)I m,]tl(~n c(~nk(,nt t~.i+ c I(w,(, to z(,ro

( d ht( )1 u tt iJ.11 N(’ 1(++ th.] n o ~.; I I n o 5 p~rc en t (I} ,11 I t ,IM\

consecutive patients presenting at an emergency

ward with complaints related to the chest were

-followed prospectively. Their clinical signs,

symptoms, and some risk factors were recorded,

and the relationship between these findings and

the X-ray results was studied. In patients over

40 years of age, 37 percent of X-rays taken

in those with normal physical examinations

showed acute radiographic findings such as

enlarged heart, pneumonia, plural effusion, and

congestive heart failure. In younger patients

without positive clinical signs, only 4.8 percent

of all X-rays had acute findings (most frequently

pneumonia). If X-rays had been withheld from

younger patients (under 40) with normal physical examinations, 16 percent of the X-rays

would have been avoided, while approximately

1.5 percent of acute radiographic X-ray findings

would have been missed. These cases (typical

pneumonia) were clinically important, however,

and the authors recommended that X-rays be

provided if symptoms persist in the younger

group.

The high yield of abnormal chest X-ray findings in symptomatic patients may explain why

the use of chest X-rays in this patient group is

not controversial. The seriousness of some findings and the importance of therapy to the outcome of diseases like pneumonia justify the presumption that the benefits in lives saved or reduced morbidity outweigh the cost of X-rays,

particularly in older patients with chest complaints who present at emergency rooms.

Studies of Radiological Method

Potential variations in radiological method

can affect diagnostic efficiency, diagnostic yield,

costs, and outcomes to differing degrees for each

diagnostic or screening application of the chest

X-ray. The type of equipment and film used, the

number of views taken, technician competence,

number and competence of readers, and access

of readers to patient information are all potentiall y important aspects of radiological method.

Because the way jn which these elements are

combined is important in assessing the validity

of an X-ray evaluation study, such information

should always be given in the study results. Un-
28 • Background paper #5: Four Common X-Ray Procedures: Problems and prospects for Economic Evaluation

fortunately, this is not always easy. Retrospective studies often are unable to determine these

elements from the medical record. Nevertheless,

inherent in any evaluation study is the question

of whether the results would have differed significantly had the method varied.

The question of radiological method has been

addressed directly in a few studies. Sagel and his

colleagues (105) investigated the usefulness of including the lateral view in addition to the frontal

view in routine hospital admission chest X-ray

examinations (105). In a retrospective study of

over 10,000 chest X-ray examinations, the additional information provided by the lateral view

was assessed. For patients between 20 and 39

years of age without reasonable possibility of

chest disease, a potentially serious abnormality

was seen only on the lateral view and not on the

posteroanterior film in only one case (0.05 percent). When chest disease was considered a possibility, the additional diagnostic yield uniquely

contributed by the lateral film was 2 percent. In

older patients (40 and above) with no suspicion

of chest disease, the additional yield of the

lateral field was 0.9 percent. The authors concluded that chest X-ray examinations with

lateral views should be limited to older patients

and those with a reasonable probability of chest

disease.

One cannot assess the validity of this recommendation without knowing more about the implications for outcomes of the abnormalities uncovered, It must also be assessed in light of the

question of the need for a chest X-ray at all in

routine hospital admissions.

The optimal number of readers of chest X-ray

films has been addressed by a number of authors, particularly those interested in the screening uses of chest X-ray (60). Radiological findings are interpretive; as such, they are subject to

observer error both in false positives and false

negatives. A false positive will entail additional

followup and possibly even inappropriate therapy, whereas a false negative can deny or delay

the initiation of needed therapy, Retrospective

studies of TB X-ray screening programs showed

that between 20 and 30 percent of positive cases

were missed by single reading (60). Adding an

independent second reader, however, increases

the probability of false positives.

Inherent in any dual-reader configuration is

the need to resolve disagreements, Arbitration,

independent third reader with majority vote,

“believe positive” or “believe negative” are examples of such rules. Hessel, Herman, and

Swenson (60) have analyzed the effect of alternative methods for resolving reader disagreements on the ultimate accuracy of chest radiographs with two readers. Using the results of independent readings by eight radiologists on 100

randomly selected chest radiographs, accuracy

increased from 43.3 percent with an individual

reader to 50 to 54,7 percent under dual-reader

systems with various schemes for resolving disagreements. Specific methods for resolving disagreements had differential effects on the falsepositive and false-negative rates. Consequently,

the best method of resolution would depend on

the implication of each of these two kinds of

errors on patient outcomes and costs.
4

Skull X-Ray
4.

Skull X-Ray

UTILIZATION, COSTS, AND CONTROVERSIES

In 1970, approximately 4.2 million radiographic skull examinations were performed,

representing 3 percent of the total number of

X-ray examinations in the United States in that

year. Over 86 percent of these procedures were

performed in hospitals (27). The average number of films used per examination was four, and

in 1970, the median gonadal dose per exam for

both sexes was less than 0.5 millirad. The bone

marrow dose was in the medium range, at 78

millirads per exam.

Skull X-rays are

uate abnormalities

strong evidence of

ordered to detect and evalof the head. They provide

skull fracture and in some

cases provide clues about abnormal intracranial

conditions. They have held a traditional place in

the evaluation of patients with head injury or

sudden onset of unconsciousness or coma.

Physicians’ claims for skull X-rays performed

on California medicaid patients in 1978 are

shown in table 8. The limited skull examination

plays a minor role in radiologic practice in

California. Over 85 percent of skull examinations were comprehensive. Comparing this table

with claims by physicians shown in table 9 reveals that radiologists perform most hospital

skull X-ray procedures but only 38 percent of

such examinations performed in physicians’ c) ffices.

In the past decade, the skull X-ray has been

criticized as an overused and not very valuable

radiological procedure (1,66,85,107). This criticism has stemmed from studies demonstrating

the low yield of positive skull X-rays (9) and low

sensitivity of the skull X-ray in detecting clinically important intracranial abnormalities such

as subdural hema torna (114) and cortical a trophy (119); from the general unimportance of detecting a fracture in the absence of any clinical

evidence of intracranial damage (58,64); and

from the arrival of a noninvasive diagnostic imaging technology that offers vastly superior inTable 8.— Medicaid Skull X-Ray Claims in California Submitted by Physicians in First Quarter

of 1978, by Location of Service

Inpatien t

a - Out patienta Office ‘ Other Total

70250 Skull: Iimited. ., 353–(2 1.7 %) 403 (10.8°f0 ) 893 (14.6%) 55 (07.7%) 1,704 (14.0%)

70260 Skull: complete 1.274 (78.3°/0) 3,319 (19.2%) 5,219 (85.4%) 657 (92.3%) 10,469 (86.0°0)

Total. . 1,627

.- -.

-

3,7 2 2 6,112 ‘

-

71 2 12,173 — . - — —

aRecorded only *hen hospital and physlc,an btll separately for Ihe service Ispl Il bllllng arrangement)

SOURCE Urban Institute sample of 5000 solo practltloners, lncludlng 177 rad(ologlsts

Table 9.—Medicaid Skull X-Ray Claims in California Submitted by Radiologists in First Quarter

of 1978, by Location of Service

Inpatient a Out patienta Office – Other Tot al

7025 0

- Skull. Iimite d 323-

(21.3% ) 400 (1 2,40/’) ‘-195 (08.4%) 409 (84.3%) 927 (12 30. )

70260 Skull: complete, ., 1,192 (78.7%) 2,836 (87.6%) 2,125 (91.6°6) 76 (15. 7%) 6,629 (87.7%)

Total ., . . ., . ., ., 1,515 3,23 6 2,32 0 4 8 5 7,55 6

aRecorded only when hosp( tal and phystc, an bI (I separately for the serv(ce ISpl II b I Ihng drrangernent]

SOURCE Urban Inst t ute sample of 177 SOIC rad!oloq ISIS 1326 percent of al I solo radlologl sts I n Cdl lfornla}

31
32 ● Background Paper #5: Four Common X-Ray Procedures: Problems and Prospects for Economic Evaluation

formation on intracranial disease and injury, skull radiographic examinations, are examined

namely, the computed tomographic (CT) scan- by CT instead. In one hospital, it was reported

ner (68,126). that 24 percent of patients suffering from acute

head injury were spared a skull roentgenogram Although there are no national data showing

the extent to which the use of the skull X-ray has after the introduction of CT (126). Even without

been affected by these factors, anecdotal evi- CT scanning, policies regarding skull X-rays in

dence from a few institutions with CT scanners two emergency rooms reduced the rate of use of

the procedure by 29 percent (99,100). indicates that many patients, particularly head

trauma victims who would have been given

SKULL X-RAY EVALUATION

The evaluation literature has had an

tant place in framing the debate about

importhe appropriateness of the skull X-ray. Two kinds of

studies have provided evidence about the usefulness of this procedure: 1) studies of diagnostic

efficiency, and 2) studies of high-yield criteria

for ordering skull examinations in emergency

rooms.

Diagnostic Efficiency of

Skull X-Ray Examinations

The diagnostic efficiency of a radiologic test

can only be assessed in terms of the diagnoses of

interest. If one is concerned with the diagnostic

efficiency of the skull X-ray in detecting skull

fractures, then the skull X-ray is generally the

definitive test. Except for examination during an

operation or postmortem, there is generally no

other method for determining whether a skull

fracture exists. Thus, for skull fractures, the

observed true-positive rate of the skull X-ray approaches 100 percent. Specificity (true-negative

rate) is also presumably high.

The diagnostic efficiency of the skull examination becomes more questionable when one considers other, more clinically significant, diagnoses. Except for depressed fractures, which

sometimes require surgery, the mere presence of

a fracture is unlikely to influence therapy in

head injury patients. The more important question is how well a test can detect intracranial abnormalities. Here, the skull X-ray does not perform well.

In a 1971 study of 100 patients with acute subdural hematoma, Talalla and Morin reported

the findings of skull X-rays taken in 50 of these

cases (114). * While 60 percent of the skull X-rays

were abnormal, in only 5 percent of the examinations was a subdural hematoma identified.

The rest showed fractures or other abnormalities

unspecific to the diagnosis. A similar study of

subdural hematomas of traumatic origin in

England showed that for those cases where a

skull X-ray was performed, the positive rate was

48 percent for simple hematomas and 80 percent

for complicated hematomas (64).

These pre-CT studies cast doubt on the ability

of the skull X-ray to differentiate between patients with and without serious injury. A later

study comparing the skull X-ray examination

with CT scanning in patients with head trauma

draws an even sharper picture of the limitations

of the skull examination.

The results of skull examinations taken in 76

percent of 285 consecutive acute head trauma

patients who received CT examinations were recorded by Zimmerman and his colleagues (126).

Of those patients with CT evidence of significant

intracranial abnormality, skull films were normal in 31 percent of children and 33 percent of

the adults. Of those patients with negative CT

* Skull X-rays were not tahen in urgent sltuatlons, or when the

patient did not survive long enough, Thus, the ettlciency of skull

X-ray is probably underestimated for the population as a whole.

However, since the procedure is only feasible t(~r the subset ~>t pat ients who did receive it, this group should be ct~nsidered representative of the relevant population,
Ch. 4—Skull X-Ray Ž 33

scans, 23 percent of the adults and 32 percent of

the children showed fractures on the skull

film. * If intracranial damage is considered, it appears that approximately one-third of abnormal

skull examinations are unrelated to the diagnosis

of interest. In detecting significant intracranial

damage, CT scanning is the definitive procedure

in the same sense that the skull X-ray is for fracture.

Even lower estimates of skull X-ray sensitivity

were obtained in studies of patients with nonacute problems suggestive of intracranial disease. A study of patients admitted to a psychiatric hospital with symptoms suggestive of

organic brain disease showed that the skull

X-ray was abnormal in only 6 percent of cases

found to be abnormal by CT scanning (119). A

comparative study of skull radiographs, CT

scans, and radionuclide bone scans in detecting

cancerous metastasis to the skull (calvaria)

showed that the skull X-ray detected only 55

percent of the calvarial metastasis identified by

one or more of the three procedures (68). The

skull X-ray was uniqueIy responsible for the detection of 1 of the 32 total calvarial lesions.

Were it not for the difference in the cost of the

skull X-ray and CT head scans, the evidence

comparing the diagnostic efficiency of skull

X-ray and CT scanning in identifying intracranial abnormalities would argue for virtual replacement of skull films by CT scans in the conditions studied. However, the technical cost of a

skull examination was estimated at about 1] percent of that of a CT examination in 1977 (48).

Consequently, the appropriate place of these

two examinations in the applications discussed is

not so straightforward. At the very least, it may

be argued that head injury patients who received

CT examinations should not also receive skull

X-rays as a routine procedure.

High-Yield Criteria for Skull X-Rays

Historically, skull X-ray examinations have

been used as a standard radiological procedure

*Because the patient populations included only those for whom

a CT scan was ordered, patlen ts who are bound to be sicker than

most, results probably overestimated the sensitivity of the sku!l

X-ray and underestimated it~ specificity, although the magnitude

of the effect is not known.

in the evaluation of patients with head injury.

Over time, the procedure has come to be viewed

as necessary to the provision of quality care, and

it has been claimed that many such examinations

are ordered by emergency room physicians for

medico-legal reasons or because the patient or

patient’s family request it, and not because the

physician sees the examination as contributing

greatly to his or her information (1,66). T h e

yield of abnormal findings in skull X-rays ordered in this way is low. Studies of diagnostic

yield in hospital emergency rooms in this country and in Britain have reported rates ranging

from under 2 percent to about 8.5 percent (9,

32,36). It is not surprising, then, that the search

for criteria for ordering skull X-ray procedures

to improve diagnostic yield would have begun

with the emergency skull X-ray.

The first attempt to determine which presenting signs, symptoms, or risk factors would be

good predictors of an abnormal skull X-ray finding was reported by Bell and Loop, who identified 21 objective and subjective findings present

in at least 10 percent of positive skull X-ray examinations obtained in 1,500 consecutive skull

examinations in two hospital emergency rooms

(9). These 21 attributes, termed “high-yield findings, ” included such elements as presence of unconsciousness for more than 5 minutes (present

in 41 percent of all skull fractures found by radiograph); discharge from the ear (present in 30

percent); accident at work or gunshot wound

(present in 15 percent); and serious suspicion of

a fracture (present in 76 percent).

Only one patient with a positive skull fracture

did not have at least one of the high-yield findings, and the radiograph made no difference to

the management of the patient’s care. Had skull

X-ray examinations been limited only to those

patients with the high-yield findings, however,

approximately 29 percent of the 1,500 patients

would not have had the examination.

The performance of the 21 high-yield findings

was recently studied in a sample of 594 cases of

head trauma in a military hospital’s emergency

room (32). Of the 17 skull fractures detected, 7

had none of the high-yield findings. All 7 were

children under 17 years of age. The patient sam1 – 1.
34 ● Backround Paper #5: Four Common X-Ray Procedures: Problems and prospects for Economic Evaluation

ple in this study was 55 percent children, compared to 9.7 percent in the Bell and Loop study

(9), indicating that in children there may be a

different relationship between symptoms and

X-ray results. With one exception, none of the

high-yield findings was significantly correlated

with positive skull radiographs (p 0.10), but

the authors did not report on the number of radiographs that would have been saved had the

criteria been applied to the patients in the study.

A recent British study of 504 head injury patients found that six of the nine skull fractures

contained one or more of just seven findings:

headache/concussion, vomiting, loss of conscious, focal or general signs of central nervous

system involvement, scalp hematoma, scalp laceration, and ear bleeding (36). These findings

were selected arbitrarily by the authors, and

their performance in terms of saved radiographs

was not assessed.

The fundamental weakness of studies of highyield criteria for skull X-rays stems from their

emphasis on diagnostic yield in the face of overwhelming evidence that X-ray findings in patients with head injury mean very little to patient management. Detection of a fracture is useful only to the extent that it indicates potential

cerebral damage. Those with serious intracranial

injury often have no fracture, while those with

fracture and no other clinical findings frequently

require no management save observation (36,

58). In some areas, hospital admission for observation is automatically prompted by a positive

skull X-ray (36), thus raising the costs issuing

from the use of this procedure on all head injury

patients.

One must question the use of a method such

as high-yield criteria to reduce the number of examinations of a procedure that offers little information relevant to therapy when the more appropriate strategy may be to eliminate skull

X-rays altogether in favor of CT scanning,

which directly detects the important conditions.

Because CT scans are expensive, however, identification of high-yield criteria for ordering CT

scans on head injury patients is of utmost urgency. One such study has been performed to date

(57).
5 ■

Barium Enema
5 ■

Barium Enema

UTILIZATION, COSTS, AND CONTROVERSIES

Barium enema (BE) is a generic term referring

to radiological studies of the colon and rectum

using contrast materials. The conventional procedure, sometimes called a single-contrast enema (SCE), consists of fluoroscope-guided radiography of the colon while it is filled with a

barium contrast solution. The double-contrast

enema (DCE) is performed while a thin layer of

contrast solution coats the colon lining and air is

insufflated into the colon. The purpose of the BE

examination is to detect diseases of the colon,

principall y colitis, regional enteritis, diverticulitis, polyps, and carcinoma.

In 1970, an estimated 3.5 million BE examinations were performed in the United States.

About 80 percent were performed in hospital

settings (31), The examination involves a high

radiation dose because of the multiple views and

the need for fluoroscope to localize the spot

films, It is estimated that in 1970, there were an

average 3.9 films per examination. As might be

expected, because of the direct exposure of the

gonads to primary beam irradiation, the BE has

a higher gonad dose for both sexes than do the

chest and skull exams. For males, this dose is 22

millirads per exam (a medium dose); for females

it is 574 millirads. For females, only the lumbar

spine exam results in a higher gonadal exposure

(28).

Of all physicians, radiologists predominate in

the administration of BE regardless of the setting

in which they are performed. Tables 10 and 11

present data on the California medicaid claims

for BE examinations. In California in 1978, 97.8

percent of all physicians’ claims for BE to the

medicaid program were filed by radiologists.

Virtually 100 percent of all physicians’ claims for

BE on inpatients and outpatients were submitted

Table IO.— Medicaid Barium Enema Claims in California Submitted by Physicians in First Quarter

of 1978, by Location of Service

SOURCE Urban Inst!tute 1980 Sample of 5000 solo pract(tloners Includtng 177 radiologists

Table 11 .—Medicaid Barium Enema Claims in California Submitted by Radiologists in First Quarter

of 1978, by Location of Service

— —Total — ——

5,040 (84.50/. )

3 7
38 ● Background Paper #5: Four Common X-Ray Procedures: Problems and Prospects for Economic Evaluation

by radiologists; almost 97 percent of claims for

BE examinations in physicians’ offices were

made by radiologists. *

The conventional SCE is much more frequent

than the more involved double contrast or combined studies. MacEwan reported that in Canada’s Manitoba Province in 1974, 95 percent of

all BEs were SCES (77). California medicaid

claims data from a sample of approximately

5,OOO solo practitioners substantiate the dominance of the conventional examination over

DCE but reveal a slight decline in its proportionate use from 1973 to 1978.** In this sample of

physicians, SCE exams accounted for 86.2 percent of BE procedures performed in physicians’

offices in 1973; by 1978, this proportion had diminished slightly to 84.1 percent. The relative

proportion of conventional BE to air-contrast

procedures decreased more appreciably in other

settings. From 1973 through 1978, the use of

SCE examinations declined from 96 to 89 percent in inpatient settings, and from 94.5 to 83

percent in hospital outpatient settings. An earlier survey of leading institutions and practitioners found a similar trend. The number of radiologists using only the DCE increased between

1966 and 1968 (84).

BE is a complicated procedure for both the patient and physician. Adequate preparation of the

patient to insure complete evacuation of fecal

matter must precede the application of the contrast enema. This preparation usually involves

dietary restriction for 1 to 2 days, administration

of cathartics, and cleansing enemas (82). Inadequate or hasty patient preparation seriously

compromises the ability to diagnose accurately

(82,91).

The radiologist is faced with numerous other

choices in technique, ranging from patient positioning to methods for compressing the colon.

One textbook states that “probably no two radiologists perform the barium enema in exactly

the same way, [but] opinion and practice on

most of the important steps of the examination

are amazingly uniform” (82).

The importance of radiological method, particularly patient preparation, to the success of

the BE implies high variation in diagnostic efficiency among physicians and facilities. This variation presents an important evaluative dilemma. If the procedure does not perform well

in a study, critics are quick to argue that radiological technique was inadequate (3). If BE is

not evaluated at its best, physicians will be

loathe to accept study findings, in the belief that

the performance in their own institutions will

surpass that of the study. However, evaluating

performance of the BE only in the best centers,

as advocated by some (3,72), may overestimate

its general value as a diagnostic tool.***

BE is well established as the mainstay of diagnostic methods in the colon (59). The development of flexible fiberoptic endoscopy of the colon (colonoscopy) in the past decade has increased the ability to detect certain diseases of

the colon, but the high cost of colonoscopy relative to BE and the general reliance of colonoscopists on prir BE films to guide their own examinations imply that the BE will not be replaced by endoscopy to any significant degree in

the foreseeable future (92). Indeed, the potential

for conflicting findings on the two examinations

may lead to increasing numbers of followup

X-ray procedures.

In recent years, investigators have used the

findings of colonoscopy to assess the sensitivity

of BE in detecting polyps and carcinomas of the

colon. Prior to the availability of colonoscopy,

the sensitivity of BE could only be surmised,

since there was no independent method for demonstrating false negatives from BE. Now, at least

some tumors and polyps not found on BE have

been found by colonoscopy. The results of these

studies of the diagnostic efficiency of BE and colonoscopy are discussed later in this section.

At present, radiologists disagree about

whether and where the DCE should be used instead of, or in addition to, the single-contrast

procedure (69,83). The choice between the SCE

and the DCE is important for medical cost and

radiological risk. The DCE examination is gen-

*Urban Institute, unpublished data, 1980.

* ● Urban Institute, unpublished data, 1980

* ● *This general issue of “efficacy” v, “effectiveness” has been

discussed elsewhere (97).
Ch. 5—Barium Enema ● 39

erally more time consuming than the SCE and

requires careful patient preparation. If both procedures are performed, costs and radiation exposure to the patient are almost doubled, The

DCE procedure appears to be more sensitive

than the SCE in detecting polyps and carcinomas

when patient preparation has been meticulous

(69), but reliability is claimed to be low in less

ideal situations (82). Some radiologists believe

that the DCE procedure should be used routinely

instead of the SCE except in certain contraindicated situations; others believe that it should

be a standard second procedure; still others believe that it is indicated when the conventional

examination gives unsatisfactory or equivocal

results (82). Often, a combined procedure of

SCE followed by partial evacuation of the contrast solution and performance of an air study is

done, but the barium contrast solution used for

the single-contrast procedure is not ideal for a

double-contrast procedure (82). Some recent

studies of the diagnostic efficiency of the SCE

and DCE have shed light on the issue. They are

reported later in this section.

Because BE remains the only practical first test

for comprehensive investigation of the colon in

patients with signs or symptoms suggestive of

colonic disease, it is particularly suitable for the

high-yield criteria evaluation technique. One

such study is described later in this section.

The Diagnostic Efficiency of BE

The ability of various diagnostic procedures

to detect the existence of color-tic polyps is of

great interest because of the presumption that a

large proportion of colon cancers originate in

polyps (33). About 100,000 new cases of colon

cancer are diagnosed each year; if they are detected while localized, 5-year survival rates are

high. Otherwise, patients have about a 17-percent 5-year survival rate (47). The detection and

subsequent monitoring or removal of polyps is

viewed by some as the best available method of

cancer control.

Table 12 presents a summary of studies of the

sensitivity of BE in detecting colonic polyps. The

recent studies of the number of colonic polyps

missed on BE but found on subsequent colonoscopy have two important findings. First, the

double-contrast examination appears to b e

much more sensitive than the standard examination in detecting polyps, especially small lesions.

Second, as polyp size increases, the sensitivity of

the double-contrast examination approaches

that of colonoscopy. Though the studies from

which these conclusions were drawn suffer from

serious design flaws, these findings are too pervasive and strong to be discounted.

What do these finding imply for the use of BE

in the detection of polyps? Unfortunately, the

information is incomplete. We do not know how

the DCE and SCE compare on specificity. If the

DCE examination were to yield a very high proportion of false-positive results, thereby necessitating more expensive followup, its apparent

superiority to the SCE would need to be explored further. Nevertheless, at this time, in patient groups for which the detection of polyps is

the goal, the double-contrast examination appears to offer greater diagnostic efficiency.

These studies can also be interpreted as measuring the additional contribution of colonoscopy to the detection of polyps. Does a colonoscopy following a BE make a significant contribution to polyp detection? BE sensitivity results

presented in table 12 indicate that colonoscopy

offers large proportional improvements in sensitivity only for small polyps. Current evidence

suggests that polyps less than 1 cm in size have a

1- to 2-percent incidence of cancer (3). Thus,

only 1 or 2 in 1,000 of the small polyps missed

by BE could be expected to be cancerous. This

additional yield of extra cancers would have to

be considered against the high cost of colonOscopy.

Several important limitations Of the design are

common to all of the studies summarized in the

table. * First, each was subject to serious patient

selection biases. Patients with negative BEs

whose physicians saw no reason to refer to colonoscopy were excluded from every study. In

one study, the only patients selected were those

‘The \tLldieS also have been criticized t)n tht, ~r(,~jnt] that the colonoscopists had access t[~ BE f’]ndinxs bd[~re performlnx thclr (~t~n

examinations (3, 72). Ekca uw the stud Ies werx, n (>t Intended t(> L I>m -

pare colonoscop}’ and BE as direct substitute~ t~~r another th]~ c r]t -

icism is of no concern ht, rt’.
40 ● Background Paper #5: Four Common x-Ray procedures: Problems and Prospects for Economic Evaluation

Table 12.—The Sensitivity of Barium Enema in the Detection of Polyps

Year(s) of

Study a

data collection Patient sample

Thoeni and 1974-76 210 patients undergoing

Menuck (1 16) colonoscopy subsequent

to barium enema (BE)

Definition of

sensitivity

Proportion of confirmed polyps

detected by test Polyps were

confirmed by one or both examinations If seen on BE and

not found on colonoscopy,

repeat BE confirmed

Proportion of confirmed polyps

detected by X-ray

Reported

sensitvity

DCE 8830,0

SCE 54 8°1,

Study design

Colonoscopists had results of BE

at hand

BE technique not standardized

Both DCE and SCE performed

Laufer, et al (71) 46 patients undergoing

colonoscopy as followup

to positive DCE

Colonoscopists had results of

DCE at hand

DCE 94%

DCES were performed at single

Institution with standard technique.

Confirmed polyps defined as

Identified on both DCE and coIonoscopy, or on subsequent endoscopy or subsequent DCE examination

Proportion of confirmed- polyps

detected by BE

Liencke,

et al (72)

1971-74 64 patients undergoing

colonoscopy subsequent

to BE

Colonoscopists had results of BE

at hand

< 5mm In size

BE 4400

BE technique not standardized,

not performed at single lnstitution

Colonoscope commonly used to

arbitrate presence or absence of

polyps, except when multiple

X-rays, colonoscopic examinations or surgical examinations

available

5mm.1cm In size

BE 440/0

Results were not reported accord.

ing to type of BE examination

performed

1 2cm In size

BE 77°4

2 or more cm In

size

Patients who had technically unsuccessful colonoscopies were

excluded from study BE 93%

Williams, et al (122) 1974 182 patients referred for < 5mm In size

colonoscopy because of

positive BE or unexplain.

ed bleeding with a normal

BE

Colonoscoplsts had results of BE

at hand

Proportion of confirmed polyps

detected by BE DCE. 730/0

BE technique not standarized SCE 13%

● about 50% performed at same

Institution with DCE

. the rest were referred from

other hospitals, most were SCE

A polyp was confirmed if found

on colonoscopy If reported on

BE and not on colonoscopy, was

assumed to be false positive due

to poor preparation

5mm- 1cm In size

DCE 87%

SCE 40%

1cm 2cm in size

DCE 99%

SCE. 75%

> 2cm in size

DCE 950/.

SCE 79%

Wolff, et al (124) . 500 patients referred for BE 80%

endoscopy after one or

more BEs

Colonoscopists had results of BE

at hand.

Proportion of polyps confirmed

by colonoscopy found on BE

Referrals for con firmation of abnormality classification

aN Umbers ,n Parentheses refer to references In ;he-llst that appears at the end of th Is background Pa Per

with positive DCE examinations, The net effect

is that the sensitivity of the X-ray examination is

overestimated, because some lesions were undoubtedly missed in the group that was not referred. The extent of the overestimation is unknown, but the problem is more troublesome for

small polyps.

nostic efficiency typical of a

rather than of performance

center.

community center

at an outstanding

These limitations do not negate the central implications of this literature: If a patient is suspected or at risk of colonic polyps or cancer, and

if X-ray studies are planned, the best approach is

a DCE followed by colonoscopy only if the

X-ray examination is positive or suggests the

need for further workup. * Though formal analyses of the costs of the single-and double-contrast procedures and of colonoscopy were not

conducted, this result is based on implicit assessIn all but one study, the BE technique was not

standardized. The X-rays were performed in different hospitals or facilities from the place of the

colonoscopy. Patient preparation was not controlled or even monitored. While this lack of

control makes it difficult to judge the quality of

radiologic method, it may also mean that the

findings are more representative of the diag-

*This conclusion must be tempered by recognition of the differences in competence in the conduct of DCE.
Ch. 5—Bar/urn Enema ● 41

— — .

ment of the cost of the three procedures in relation to their diagnostic efficiency. Notice, however, that the findings do not reveal the conditions under which the benefit from either kind of

X-ray study of the colon is worth its costs.

What patient signs, symptoms, or risk factors

are likely to correlate highly with the existence

of polyps, particularly large polyps or carcinomas of the colon? What are the ultimate

benefits and costs of offering the double-contrast

examination to these or other kinds of patients?

These questions have not been addressed in the

literature.

A recent study of the diagnostic efficiency of

DCE in rectal cancer illustrates the limitations of

diagnostic efficiency as the evaluative endpoint.

The rectum has long been considered the province of the rigid sigmoidoscope, a relatively inexpensive and wide] y available diagnostic instrument. (In 1980, California’s medicaid program paid $13.17 for a proctoscopy compared to

$39 for a DCE. ) SCE has never been particularly

suitable for visualization of the rectum. With increasing acceptance of the double-contrast technique, however, the ability of X-rays to detect

lesions in the rectum has increased markedly.

Evers and her colleagues reviewed the records of

go cases of cancer of the rectum in two institutions which routinely use the double-contrast

method (3.5 ). In 66 of those cases, both proctoscopy and DCE were performed, although

which came first and whether the results of the

earlier precedure were available to those who

performed the later procedure were not known.

The observed true-positive rate of the DCE was

91 percent, while that of proctoscopy was 86

percent. Should patients presenting with symptoms suggestive of rectal carcinoma (constipation and bleeding) be examined by DCE instead

of, or in addition to, the proctoscope? The results of the study are insufficient to answer this

question, although the authors concluded that

“the rectum is the province of the radiologist”

(35 ). The specificity of the two examinations,

the number of true-positive cases that would be

found and the stage at which they are detected,

the ultimate effect on survival, and the cost of

the examinations and subsequent medical care

would have to be known to fully understand the

implications of an affirmative or negative response to the question.

High-Yield Criteria for BE

Gerson and colleagues have recently reported

on an attempt to apply a high-yield criteria

method to SCE (49). The study was intended to

identify symptoms, signs, and laboratory findings which could be used as criteria for referral

to SCE. Physicians referring patients to a university-affiliated radiology department for SCES

over a 22-month period in 1974 and 1975 were

required to fill out a requisition form containing

information on over 40 specific patient attributes—signs, symptoms, and laborator y findings. The presence or absence of these findings

was correlated with the outcome of the BE examination, An attribute was included in the highyield criteria set if its likelihood ration, L,, was

significantly greater than 1. Ll was defined as

follows:

When all attributes with values of L significantly greater than 1 were identified, the “highyield” set was considered complete. Only five

findings were so identified: rectal mass, fever,

abdominal mass, low hematocrit, and positive

stool benzidine (a test for blood in the stool).

Had these criteria been used in the sample of patients studied, 36 percent of the BEs would have

been avoided, but 22 percent of diseased patients

and 10 percent of those with cancer would have

been missed. Thus, the high-yield criteria so

selected did not perform well, especially since an

even greater deterioration in performance could

be expected in other patient samples.

Although these results are disappointirig, they

do not provide definitive evidence against the

use of high-yield criteria; performance may have

been improved by using other methods or statistical approaches. If performance were to remain

low after reanalysis, however, this would suggest that the symptoms suggestive of colonic

disease are also suggestive of other problems,

and that colonic disease occurs in too broad an
42 . Background Paper #5: Four Common X-Ray Procedures: Problems and Prospects for Economic Evaluation

array of

that will

symptom complexes to provide criteria

perform well.

This study also highlights a potential danger

inherent in implementing a high-yield criteria referral process for a test with such a wide referral

base (unlike skull X-rays, where the potential

population is limited to those with head injury).

Suppose, for example, that the five findings had

performed well and that they were accepted as

referral criteria for barium enemas. The presence

of fever would be one such criterion, Does this

imply that all persons or even all persons over 40

presenting with fever should be referred? Surely

not, but the mere existence of the referral list

would be likely to provoke referral of more patients with marginal clinical indications, or isolated findings, with a consequent further deterioration of diagnostic yield. MacEwan has demonstrated that the physician’s strong suspicions

(probability > 0.50) of carcinoma of the colon is

related to a high proportion of positive cases

(7’7). The Gerson study did not include such subjective criteria in its initial attribute list, but they

are probably surrogates for the existence of patterns of multiple-objective findings that are likely to occur together in the presence of disease. It

would be worth exploring how combinations of

symptoms contribute to the separation of normal from abnormal X-rays.
6 ●

Excretory Urogram
6.

Excretory Urogram —

UTILIZATION, COSTS, AND CONTROVERSIES

Excretory urogram (ExU) refers to any procedure that provides for X-ray delineation of the

urinary tract using an opaque contrast medium

injected (or occasionally infused) into the blood

(123). * As the contrast medium is excreted by

the kidneys through the urinary tract, usually

within 15 to 20 minutes of injection, the anatomy of the urinary tract organs can be delineated by X-ray films. Special types of ExU examinations, such as cystography (bladder studies)

or urethorography, focus on particular sections

of the urinary tract. The examination “must be

tailored to meet the needs of the individual patient or clinical problem” (123).

The primary purpose of ExU is to detect obstructions (calcifications, tumors, etc. ) and other

diseases in the urinary tract. ExU is also a diagnostic tool for detection of renovascular disease,

an underlying cause of hypertension in about 10

percent of hypertensive cases (13).

In 1970, approximately 3.9 million ExU examinations were performed, representing about 3

percent of the radiographic examinations performed in the United States that year. Over 85

percent of these procedures took place in hospitals, and the average number of films used per

examination was 5.3. The ExU procedure subjects the patient to a relatively high gonad dose,

and this dose is higher for women (448 millirads

per exam) than for men (20 millirads per exam)

(28).

Not only does ExU involve high radiation exposure to vulnerable organs, but the injection of

the contrast medium can cause acute reactions.

In a study of almost 33,000 consecutive patients

receiving ExUS, 1.72 percent had acute reactions; 5 percent of these developed severe or lifethreatening reactions, and one patient died

•T~t term e~cretor} ur(~~rarn I+ generally’ ud [nterchan~eabl,

\\ I th I n tra \’c,n( IU \ pve] OKraph }’ ( I ;’1 ] J but the ]~ t tt~r term IS ~ m I+

n{)mtr and IS a\’(JIded In m(dern tt,x t~ ( ] 23 )

(123). Patients with heart disease and diabetes

are at higher risk for the development of undesirable side effects such as rapid heart beat o r

cardiac arrest (10,123).

As with the BE examination, radiologists perform most ExUS. According to California physicians’ medicaid claims records for 1978,** radiologists performed 93 percent of all ExU exams

on these patients. In hospitals (both inpatient

and outpatient settings}, radiologists performed

100 percent of these exams, compared to 88 percent in physicians’ offices.

In comparing the relative frequency of ExUS,

hypertensive urograms, and drip infusion urograms, the standard procedure accounts for a

large proportion of all urograms. Tables 13 and

14 present summaries of physicians’ medicaid

claims for ExU in 1978. California medicaid data

indicated that from 1973 to 1976, the standard

ExU comprised an average Of 84.5 percent of the

EXUS performed in physicians’ offices. In outpatient settings, the proportion was similar, at an

average of 84.1 percent, and slightly lower for

inpatient examinations (81. 7 percent). The data

do not reveal any trends toward increases or decreases in the proportion of standard urograms

performed during these 4 years.

The ExU examination is uncomfortable for the

patient, and it requires some preparation, including prior dehydration and catharsis. Considered together with the morbidity, risk, and

radiation exposure inherent in the procedure,

and its cost, ExU is in little danger of becoming a

routine or screening examination. Nevertheless,

questions have arisen about the appropriateness

of its use in certain patient groups such as

women with urinary tract infections and about

the potential for simplifying radioIogic methods
46 . Background paper #5: Four Common )(-Ray procedures: Problems and Prospects for Economic Evaluation

Table 13.—Medicaid Excretory Urogram Claims in California Submitted by Physicians in First Quarter

of 1978, by Location of Service

In patienta Outpatien t

a — Office Other Total

74400 Excretory urogram. . . . . . . . . 789 (77.1 O/. ) 1,011 (71.0°/0) 4,105 (82.20/. ) 16 (84.2°/0) 5,921 (79.20/o)

74405 Excretory urogram:

hypertensive. . . . . . . . . . . . . 19 (01 .90/o) 143 (lO.OO

/O) 290 (05.80/. ) — 452 (06.0°/0)

74406 Excretory urogram:

extended. . . . . . . . . . . . . . . 139 (13.6°/0) 128 (09.0%) 286 (05.7%) 3 (05.8°4) 556 (07.5°/0)

74410 Excretory urogram:

infusion . . . . . . . . . . . . . . 76 (07.4%) 142 (lO.OO

/~) 313 (06.0°/0) — 531 (07.1 0

/0)

Total . . . . . . . . . . . . . . . . . . . . . . . . . . 1,023 1,424 4,994 19 7,460

aRecorded o y nl when hospital and physlclan bill separately for the service (split bl I Ilng arrangement)

SOURCE. Urban Inst!tute, 1980 Sample of 5,000 sole practitioners, Includlng 177 rad!ologlsts

Table 14.—Medicaid Excretory Urogram Claims in California Submitted by Radiologists in First Quarter

of 1978, by Location of Service

Inpatient a Outpatient a Office Other Total

74400 Excretory urogram. . . . . . . . . . . 706 (88.30/. ) 1,003 (77.9°/0) 2,031 (87.5%) 16 (lOOO

/o) 3,756 (84.9°/0)

74405 Hypertensive (’69 RVS). ... , . 18 (O2.3%) 143 (11 .1%) 186 (08.0%) — 347 (07.80/. )

74410 Infusion (’60 RVS). . . . . . . . . . 76 (09.5°/0) 142 (1 1.0%) 103 (04.40/o) — 321 (07.3°/0)

Total . . . . . . . . . . . . . . . . . . . . . . . . . . . 800 1,288 2,320 16 4,424

aRecorded only when hospital and physlclan bill separately for the serwce (sPllt blllln9 arrangement)

SOURCE Urban Institute, 1980 Sample of 177 sole radiologists (326 percent of sole radiologists In Call fornla)

in order to save cost and reduce radiation exposure. A few clinical evaluative studies have

addressed these issues.

The evaluative literature follows the following

broad categories: 1) studies of diagnostic yield

and high-yield criteria for ordering ExU, 2) studies of appropriate radiologic method, 3) studies

of the role of ExU in screening for renovascular

disease, and 4) studies of the information content of the ExU. Each is discussed below.

Diagnostic Yield and High= Yield Criteria

Van Woert and associates reported on a review of 200 consecutive hospital and clinic patients who had received EXUS during a 4-month

period in 1955-56 (120). Fifty-five examinations

(27.5 percent) were abnormal. The investigation

correlated ExU results with prior signs, symptoms, or findings. In 50 percent of patients with

a history of colicky pain, ExU was positive.

Other signs or symptoms found to be important

predictors of abnormality were palpable renal

mass (5o percent); hematuria (40 percent); white

blood cells in urine (25 percent); and costovertebral angle tenderness (20 percent). Moreover,

combinations of these symptoms increased the

probability of an abnormal ExU. Using this list

as a starting point, the authors constructed a set

of 10 indications for ordering an ExU. Use of the

criteria constructed in this arbitrary fashion

would have eliminated 25 percent of the 200 ExU

examinations while at the same time missing 4 of

the 55 abnormal ExU findings. In the opinion of

the authors, none of the 4 was clinically significant, It must be noted, however, that the performance of the criteria was not tested on independent patient samples.

More recently, Mellins and associates studied

over 1,622 patients referred to a major teaching

hospital for ExU (89). Referring physicians were

asked to complete a questionnaire giving information on signs, symptoms, and laboratory

findings in each patient. These attributes were

then associated with ExU findings by constructing attribute likelihood ratios. Those with likelihood ratios suggesting a significant relationship

between the attribute and ExU results were con-
Ch. 6—Excretory Urogram ● 47

sidered high-yield criteria. In patients without

known prior genitourinary disease, these highyield findings included gross hematuria (visible

blood in urine); nocturia (excessive urination at

night); elevated creatinine level; proteinuria (excess of serum proteins in urine); and elevated

BUN (urea nitrogen) levels. Had these findings

been used as referral criteria in the patient sample studied, 65 percent of ExU examinations

would have been avoided, but 55 percent of abnormal ExU examinations would have been

missed. The authors concluded that the use of

the high-yield criteria so constructed would provide an unacceptably high false-negative rate

(low sensitivity) and therefore offered no improvement over current referral processes.

An example of the potential benefits to be

derived from further studies of the contribution

of particular indications to diagnostic yield is

given in two recent studies of diagnostic yield of

ExU in women with recurrent urinary tract infection (37, 46). In the first, a review of 164 cases

in which an ExU was performed at a universityaffiliated hospital on women whose major indication for the examination was a history of recurrent urinary tract infection showed a diagnostic yield of 5.5 percent. Only one positive examination (0.6 percent) revealed a potentially

significant abnormality, but it was considered

unrelated to the symptoms of urinary tract infection. These results were supported by those of a

similar study of 104 patients referred for excretory urography (46). Although it is unknown

how frequently ExU examinations are performed

for this indication, promulgation of better criteria for ordering the procedure is likely to make

some difference to total ExU volume.

Studies of Appropriate

Radiologic Method

New variations in radiologic method are frequently tested and reported. Here, one element

of radiological method with significant implications for the cost of medical care is reviewed: the

number of films taken as part of the examination. In ExU, X-ray films are taken both before

and at specific intervals after the injection of the

contrast materials. Although these intervals

vary with the clinical problem (e. g., the sequence of films is more rapid for hypertensive

patients than for other patients), there is wide

variation in the number and timing of films used

in standard examinations,

Van Woert and colleagues addressed the question of film sequence in 1958 in a study whose

purpose was to search for ways of decreasing gonadal radiation (120). In 87 positive ExU examinations for ureteral abnormalities, films were exposed at 5-, 10-, and 15-minute intervals after injection of the contrast. In only 3 of the 87 cases

could the pathology be demonstrated on the

early films but not on the 15-minute or subsequent films; the 3 cases involved clinically insignificant conditions. Thus, in none of the 87 cases

was the 5- or 10-minute film essential to diagnosis of lower urinary tract disease. Gonadal

shielding on the early films was recommended.

It should be noted that the study was a review of

past urograms, probably with reviewer knowledge of the original findings. It is not clear how

an independent blind review of these cases in a

larger sample containing both normal and abnormal urograms would have fared in detecting

ureteral abnormalities on only the 15-minute

film.

More recently Hillman and his associates investigated the sensitivity, specificity, and accuracy of ExU exams using different film sequences

(61). Four experienced staff radiologists viewed

45 urograms, 21 normal and 24 abnormal, with

abnormal cases representing a broad spectrum

of diseases, The radiologists first reviewed a

one-film examination (15 minutes); a three-film

examination (1, 10, and 15 minutes); and a sixfilm examination (1, 5, 10, 10, 10, and 15 minutes). ’ Mean sensitivity (true-positive rate) was

93, 88, and 91 percent on the one-, three-, and

six-film urograms, respectively. Mean specificity

(true-negative rate) was 67, 77, and 80 percent ,

respectively. Accuracy was 82, 83, and 85 percent. Thus, while specificity increased with additional films, sensitivity was not affected. However, the definitiveness of disease diagnosis (i. e.,

abilit y to correctly differentiate among possible

*The six-film examinatic>n inv(>lved three different views at 10

minutes,
48 ● Background paper #5: Four Common X-Ray Procedures: Problems and Prospects for Economic Evaluation

diseases) did increase as the number of films increased (75, 85, and 84 percent, respectively).

On the basis of these findings, the authors recommended a policy of a one-film postinjection

examination (at 10 minutes) followed by reinfection of contrast if the film indicates an abnormal. The authors made a rough estimate of national annual savings of $368 million if this policy were followed. Better estimation procedures

would probably reduce this value substantially.

Nevertheless, the authors have demonstrated

that economies are possible through changes in

radiographic method without significant

changes in diagnostic efficiency.

Studies of the Role of ExU in Screening

for Renovascular Hypertension

It has been estimated that about 10 percent of

persons with hypertension have the condition as

a consequence of underlying renovascular disease (13). In particular, stenosis (narrowing) of

the renal artery is often present, and in some

cases, surgery can correct the resulting hypertension. Thus, differentiation of patients with essential hypertension (i. e., not secondary to

another condition) from those with renovascular

hypertension has been of interest to clinicians

and researchers alike. In 1961, a cooperative

study of renovascular hypertension was initiated, with the purpose of improving understanding of the disease, its detection, and therapy

(13), Consequently, a great deal of information

exists on the efficiency of alternative diagnostic

methods and outcome of therapies.

EXUS show features suggestive of renovascular

disease. The major features are a significant difference in length of the kidneys; a significant difference in the time until contrast appears at the

calyx on each side; and a difference in concentration of contrast medium on each side (13).

The difference-in-appearance time mandates a

large number of early postcontrast films. A

fairly uniform technique is to take X-ray films at

intervals of 1, 2, 3, 4, 5, 10, 15 and 30 minutes

after the rapid injection of contrast (13), The

urogram does not provide definitive diagnosis,

however. Angiography, an invasive, difficult,

and expensive procedure can be used to prove

renovascular disease. * Urography is one of several signs, symptoms, and laboratory findings

potentially useful in screening for the disease.

The central question involving the use of

urography is whether it should be used as a general or selective screening tool for detection of

renovascular disease in hypertensive patients.

Bookstein and colleagues reported on a study

of diagnostic efficiency of ExU in 198 patients

with proved unilateral renovascular hypertension and 771 cases of essential hypertension in

the Cooperative Study (12,13). The ExU falsepositive rate in essential hypertension was 11.4

percent. In patients with serious unilateral renovascular disease, the true-positive rate was 78.2

percent.

The information generated by the Cooperative Study enabled McNeil and her colleagues

(80) to perform a cost-effectiveness analysis of

two issues: 1) the relative merits of screening

hypertensives with ExU v. the renogram, a radionuclide procedure; and 2) the relative merits

of screening v. no screening for renovascular

diseases in hypertensive patients, In the former

study, the evaluative measure chosen was the

cost per surgical cure of each screening alternative. In the latter, the authors calculated the cost

of keeping a patient from incurring a morbid

event associated with hypertension for 16 years.

In the study of the ExU v. the renogram, the

cost per surgical cure was found to be $15,000

for ExU, $14,000 for the renogram, and $20,000

if both are performed. These estimates, while

based on some rather heroic assumptions about

the cost of diagnosis and treatment,** would

suggest that the renogram be considered the prim a ry screening technique.

The more germane issue is whether a general

screening program in hypertensives is worthwhile at all. Here, the alternative strategies are:

1) screening for renovascular disease by ExU,

with surgical intervention in those renovascular

‘Recent advances in angiographic techniques that allow for direct visualization of the renal arteries with less invasive methods

may make the ExU obsolete in the future.

* ● See Wagner ( Ii! I ) for a discussion of problem of co~t measurement.
Ch. 6—Excretory Urogram ● 49

.

hypertensive found to be amenable to surgery;

and 2 ) no screening and medical management of

all patients. The cost of providing an additional

well patient by the route of screening and surgery was $56,000. The cost of protecting women

is higher. Cost also increases with decreasing

diastolic blood pressures and with the rate of

compliance with medical regimens.

The success of the authors in examining the

impact of alternative diagnostic strategies on

outcomes is due largely to the availability of a

rich data base emanating from large-scale epidemiological and clinical studies. It might have

been useful to know how the morbid and mortal

events under the alternative strategies were

dispersed through time, since bad outcomes that

occur later are preferred to those that occur

sooner. Nevertheless, information sufficient to

make a decision about the usefulness of screening, and the appropriate diagnostic tools for

screening, is present. Whether $56,000 per additional well person is too high or too low a price

to pay for hypertensive screening is a political

decision fraught with questions of equity and

ethics. Should society pay to screen hypertensive in groups with historically low rates of

compliance with medical regimens? These questions can be posed only because information is

available to frame existing tradeoffs.

Studies of the Diagnostic Information

From ExU

Thornbury, Fry back, and Edwards attempted

to determine the extent to which ExU is useful in

changin~ physicians’ levels of uncertainty about

the correct diagnosis ( 117). Their study was premised on the assumption that if a test substantially alters physicians’ subjective probability

assessments, then it has diagnostic value. In a

prospective study of 67 patients referred to two

outpatient clinics for ExU, the referring physicians were asked to estimate the probability of

the most likely diagnosis prior to the test. After

the results of the ExU were received, the physicians’ ratio of posttest to pretest odds was constructed, and a logarithmic index of this ratio

was used to measure the degree of change (either

positive or negative) in these odds. An index

value of zero would denote no effect of ExU on

physicians’ probabilities. Successively higher

values would suggest larger impacts of the ExU

on diagnostic certainty. Thirty-five of the sixtyseven patients had an index value of less than

0.5, indicating little or no change in probability

estimates resulting from the information provided by the ExU. These results contrast with

those of the American College of Radiology

study, where only 34 percent of ExU examinations performed in participating emergenc y

rooms received an index value of less than 0.75

(76). The differences in the two studies could

result from inconsistencies in study designs or

differences in the patient mix.

In any case, it is difficult to draw inferences

for medical practice for these studies. The study

sample had various presenting signs and symptoms; whether the ExU is useful for some of

these and not for others was not explored.

Thornbury and his associates (117) noted that

about one-half of the cases in which no change

in probabilities was recorded were ultimately

diagnosed as essential hypertension, indicating

that these tests were performed to screen for

renovascular hypertension. Without information on the findings from all hypertension patients in the study and separate analysis of those

with other presenting conditions, these studies

are virtually meaningless.

Appendix A. —Glossary of Terms

Angiography. —Radiography of vessels after the injections of a radiopaque material.

Asymptomatic. —Without symptoms.

Calvarial.—Relating to the skull cap.

Calyx. —One of the branches of recesses of the pelvis

of the kidney.

Costovertebral angle tenderness. —Tenderness in the

ribs and bodies of the thoracic vertebrae.

Colicky pain.—Spasmodic pain in the abdomen.

Cortical atrophy .—Wasting of tissues in the outer

portion of the cerebrum.

Diagnostic efficiency. —A general term to denote the

ability of a test to diagnose correctly.

Diagnostic accuracy. —An index of diagnostic efficiency, defined as the proportion of test results that

are correct.

Diagnostic yield. —The proportion of test results that

are positive.

Evaluative endpoint. —The measure or measures

chosen to denote the effectiveness of a diagnostic

procedure.

Fluoroscope. —Use of a fluorescent screen in rendering X-ray shadows visible.

Gonad dose. –The amount of radiation absorbed by

the gonads resulting from any part of the body

being exposed to X-rays.

Hematoma. —A bruise confined to a particular organ

or tissue.

Hematuria. —Blood in the urine.

High-yield criteria. —Signs, symptoms, or risk factors occurring in a patient which are related to high

probability that a test result will be positive.

Incidence. —The rate of occurrence of a disease or

condition in a defined time period.

Information value of a test. —The ability of a test to

alter the probabilty of a disease, measured either

subjectively or objectively.

Intracranial. —Within the skull.

Likelihood ratio. —The ratio of true-positive to falsepositive test results.

Metastasis .—The shifting of a disease, or its local

manifestations, from one part of the body to

another.

Organic. —Relating to an organ.

Photofluorography. —Fluoroscope; the recording on

film of fluoroscopic views.

Polyp.—A general term for any mass of tissue that

projects outward from normal surface tissue.

Prevalence. —The relative frequency of a disease or

condition in a population at any point in time,

Prospective studies. —Studies that follow patients

and collect research data during the course ok treatment.

Rad.—Radiation absorbed dose, or the energy absorbed at a particular point in a substance.

Radiogram. —A record made by means of X-rays ~>r a

radioactive substance.

Radiography. —The making of a radiogram.

Radiologic method. —Techniques in radiographer

which are at the discretion of the physician, such

as number of views, positioning, choice of contrast

medium, length of exposure, patient preparation,

etc.

Renovascular disease. —Disease of the blood vessels

of the kidneys.

Risk factors .—Characteristics of an individual, such

as race, sex, age, other demographic variables, genetic variables, or aspects of lifestyle which predispose the person to a particular disease.

Roentgenograph.—Examination of any part of the

body for diagnostic purposes by using roentxen

rays (i. e., X-rays).

Screening.—Performance of a test in an individual

with no relevant symptoms.

Sensitivity .—The ability of a test to detect disease

when it is present. Measured as the proportion of

diseased individuals whose test results are positive.

Specificity .—The ability of a test to rule out disease

when it is not present. Measured as the proportion

of normal individuals whose test results are negative.

Stenosis.—A narrowing or stricture of a vessel or

valve.

Subdural hematoma.—A bruise occurring beneath

the dura, or outer envelope of the brain.

Symptomatic .—Any departure from the normal in

function, appearance, or sensation experienced by

the patient and indicative of disease.

53
Appendix

Other

B.—Description of

Volumes of the Assessment

technology, 19 case studies were prepared. All 19 are

available individually. In addition, 17 of the cases are

available collectively in a volume entitled Background Paper #l: Case Studies of Medical Technologies. Some of the cases represent formal CEAS (e.g.,

the case on bone marrow transplants), and some represent net cost or “least cost” analysis (e. g., the case

on certain respiratory therapies). Other cases illustrate various issues such as the difficulty of conducting CEA in the absence of adequate efficacy and safety information (e. g., the case on breast cancer surgery), or the role and impact of formal analysis on

policymaking (e. g., the case on end-stage renal disease interventions). The 17 case studies in Back--

ground Paper #2 and their authors are:

Artificial Heart

Deborah P. Lubeck

John P. Bunker

Automated Multichannel Chemistry Analyzers

Milton C. Weinstein

Laurie A. Pearlman

Bone Marrow Transplants

Stuart O. Schweitzer

C. C. Scalzi

Breast Cancer Surgery

Karen Schachter

Duncan Neuhauser

Cardiac Radionuclide Imaging

William B. Stason

Eric Fortess

Cervical Cancer Screening

Bryan R. Luce

Cimetidine and Peptic Ulcer Disease

Harvey V. Fineberg

Laurie A. Pearlman

Colon Cancer Screening

David M. Eddy

CT Scanning

Judith L. Wagner

Elective Hysterectomy

Carol Korenbrot

Ann B. Flood

Michael Higgins

Noralou Roos

John P. Bunker

End-Stage Renal Disease Interventions

Richard A. Rettig

Gastrointestinal Endoscopy

Jonathan A. Showstack

Steven A. Schroeder

54
Appendix B—Description of Other Volume of the Assessment ● 55

Neonatal Intensive Care

Peter Budetti

Peggy McManus

Nancy Barrand

Lu Ann LeRoy

Orthopedic Joint Prosthetic Implants

Judith D. Bentkover

Philip G. Drew

Periodontal Disease Interventions

Richard M. Scheffler

Sheldon Rovin

Respiratory Therapy

Richard M. Scheffler

Morgan Delaney

The 18th case study is Background Paper #3: The

Efficacy and Cost Effectiveness of Psychlotherapy.

The 19th case study is the present volume, Backgroung Paper #5: Four Common X-Ray Procedures:

Problems and Prospects for Economic Evaluation.

It was prepared by Judith L. Wagner, and Martha J.

Krieger.

Backround Paper #4: The Management of Health

Care Technology in Ten Countries is an analysis of

the policies, programs, and methods, including costeffectiveness and cost-benefit techniques, that nine

industrialized nations other than the United States

use to manage the effects of medical technology. The

experience of these nine countries in managing medical technology is compared to that of the United

States. The paper on the United States and the comparative analysis were prepared by OTA staff, assisted by Louise Russell. The authors of the papers on

the nine foreign countries are:

United Kingdom

Barbara Stocking

Canada

Jack Needleman

Australia

Sydney Sax

Japan

Joel Broida

France

Rebecca Fuhrer

Germany

Karin A. Dumbaugh

Netherlands

L. M. J. Groot

Iceland

David Gunnarson

Duncan vB. Neuhauser

Sweden

Erik H. G. Gaensler

Egon Jonsson

Duncan vB. Neuhauser

A related report prepared by OTA and reviewed

by the Advisory Panel to the overall assessment is A

Review of Selected Federal Vaccine and Immunization Policies. That study, published in September of

1979, examined vaccine research, development, and

production; vaccine efficacy, safety, and cost effectiveness; liability issues; and factors affecting the use

of vaccines. Pneumococcal vaccine was used as a

case study, and a CEA/CBA was performed.
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