Overview

Elevated blood pressure (BP), also termed

hypertension, is a common, powerful, and

independent risk factor for cardiovascular diseases

(CVD) and kidney disease. Approximately 25

percent of the adult U.S. population, about 50

million persons, has hypertension, defined as

current use of anti-hypertensive medication, a

systolic BP >140 mmHg, and/or diastolic BP > 90

mmHg. 

In view of the epidemic of high BP and its

complications, prevention and control of high BP

continues to be a major national health priority.

Governments, institutions, health care providers,

insurers, private industry, and non-profit

organizations have committed substantial

resources to prevent and treat hypertension. Still,

hypertension control rates have been

unsatisfactory. 

Measuring BP to diagnose hypertension and to

monitor therapy is problematic. Concomitantly,

the enormous scope of the BP problem, the high

aggregate costs of hypertension care, and the

potential for medication side effects have spawned

efforts to target therapy more effectively. This

entails identifying lower risk individuals who

might be candidates for less aggressive therapy and

higher risk individuals who should receive more

aggressive therapy. Measurement of BP outside of

the office or clinic setting by ambulatory BP

(ABP) monitoring and self-measured BP (SMBP)

monitoring might accomplish these objectives.

Clinic Blood Pressure

Measurements

BP as recorded in the office or clinic setting is

the standard technique recommended for

measurement of BP in routine medical care. The

standard technique includes use of a mercury

sphygmomanometer (or a calibrated aneroid

device or validated electronic device) and an

appropriate-sized cuff. Prior to measurement,

patients should rest quietly in the seated position

for several minutes. At each visit, at least two

readings should be obtained. Except for those

individuals with extremely high BP, the diagnosis

of hypertension and adjustments in medication

should then be based on the average of readings

across two or more visits. 

Clinic BP measurements have several

limitations, even if they are measured according to

established guidelines. First, clinic BP

measurements exhibit enormous variability, which

hinders accurate classification and which frustrates

providers and patients. Another limitation is that

BP measured in the clinic may not be a

representative estimate of usual BP outside the

clinic setting. Commonly, BP rises in the clinic

setting, in response to the observer and/or other

aspects of the medical environment. The

difference between measurements obtained in and

outside the clinic setting leads to confusion about

the diagnosis of hypertension and the need to start

or modify therapy. Unfortunately, there are

additional limitations because clinic measurements

often do not conform to established guidelines.

Specific limitations include lack of observer

training, inadequate rest period prior to initial

measurement, use of wrong-sized cuffs, rapid

deflation of cuff, incorrect position of patients,

and awkward position of the observer and/or

manometer.

Over the past several years, stationary

automated devices and aneroid devices have

increasingly replaced mercury

Evidence Report/Technology Assessment

Number 63

Utility of Blood Pressure Monitoring Outside 

of the Clinic Setting

Summary

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES • Public Health Service

Agency for Healthcare Research and Quality
sphygmomanometers in the clinic setting. Aneroid devices are

inexpensive but still require an individual, typically a health

care provider, to manually inflate a cuff and record the

appearance and disappearance of Korotkoff sounds. In

contrast, fully automated devices require minimal technical

skills, that is, only placement of a cuff and initiation of a

reading. An additional reason leading to greater use of aneroid

and automated devices stems from concerns over mercury

toxicity. 

Self-measured Blood Pressure (SMBP)

SMBP devices include mercury sphygmomanometers,

aneroid manometers, semiautomatic devices, and fully

automatic electronic devices. Automatic devices measure BP

using an oscillometric technique in which systolic and diastolic

BP are estimated from the pattern of vibrations in the cuff as it

is deflated. Fully automated devices are popular because the

patient does not have to inflate the cuff or listen for the

appearance and disappearance of Korotkoff sounds. Although

numerous, perhaps hundreds, of SMBP devices are on the

market, very few have been independently validated. 

SMBP devices provide an opportunity to record BP at

home, outside of the artificial setting of the medical office or

clinic. Ideally, the patient is trained to record BP using a

standard technique. Occasionally, physicians may observe the

patient recording a BP measurement in the clinic and then

perform a cross check of readings. The presentation of SMBP

data is extraordinarily variable. Commonly, patients at their

own initiative provide written lists of readings to their

physicians at office visits. However, recent innovations have

greatly enhanced the potential utility of SMBP devices to

synthesize and present data. Contemporary SMBP devices

have the capacity to store and download readings via phone or

computer. Data can then be synthesized and reports can be

generated and sent to the patient and/or physician. 

SMBP has several potential uses. Repeated measurements, if

averaged, should provide a more precise estimate of usual BP

than occasional measurements obtained in the clinic. As a

substitute for clinic BP, SMBP monitoring could then be used

to adjust anti-hypertensive drug therapy and thereby reduce the

need for frequent clinic visits and their associated costs and

inconvenience. The extent to which physicians, or patients, use

SMBP data to adjust medication is unclear. In addition, selfmeasurement of BP has also been proposed as a means to

improve adherence with treatment. 

Self-measurement of BP theoretically provides a means to

diagnose white coat hypertension (WCH), also termed nonsustained or office hypertension. This pattern refers to an

elevation of clinic BP in the hypertensive range but normal or

low BP outside the clinic setting. Individuals with WCH may

be at comparatively low risk for BP-related complications in

comparison to individuals with sustained hypertension. An

important issue is whether the risk of WCH exceeds that of

nonhypertensives.

Ambulatory Blood Pressure (ABP)

Measurement

ABP monitoring is a noninvasive, fully automated technique

in which BP is recorded over an extended period of time,

typically 24 hours. The required equipment includes a cuff, a

small monitor (attached to a belt), and a tube connecting the

monitor to the cuff. Usually, a trained technician places the

device on the patient, provides instructions to the patient, and

then downloads data from the device when the patient returns.

Most ABP devices use an oscillometric technique. Compared

to SMBP, relatively few ABP devices are on the market.

However, in contrast to SMBP devices, most currently available

ABP devices have undergone validation testing, as

recommended by the American Association of Medical

Instrumentation (AAMI) or the British Hypertension Society

(BHS). 

During a typical ABP monitoring session, BP is measured

every 15 to 30 minutes over a 24-hour period (including both

awake and asleep hours). The total number of readings usually

varies between 50 and 100. BP data are stored in the monitor

and then downloaded into device-specific computer software.

The raw data can then be synthesized into a report that

provides mean values by hour and period (daytime [awake],

nighttime [asleep], and 24-hour BP), both for systolic and

diastolic BP. The most common output used in

decisionmaking are absolute levels of BP, that is, mean daytime,

nighttime, and 24-hour values. Because of the expense of ABP

equipment (up to $5,000 for a monitor, cuff set, and software),

the requirement for technicians, the inconvenience and logistics

of placing and removing ABP devices, and, until recently, the

lack of reimbursement, it is uncommon for ABP monitoring to

be done frequently. However, use of ABP will likely increase as

a result of the decision by the Centers for Medicare and

Medicaid Services (CMS) to cover ABP in selected settings,

namely, the identification of WCH.

In addition to mean absolute levels of ABP, certain ABP

patterns may predict BP-related complications. The patterns of

greatest interest are WCH and nondipping BP. Using both

daytime and nocturnal ABP, one can identify individuals,

termed nondippers, who do not experience the decline in BP

that occurs during sleep hours. Usually, nighttime (asleep) BP

drops by 10 percent or more from daytime (awake) BP.

Research has suggested that individuals with a nondipping

pattern (less than 10-percent BP reduction from night to day)

may be at increased risk of BP-related complications compared

to those with a normal dipping pattern.

2
Although ABP could be used to monitor therapy, the most

common application is diagnostic, that is, to ascertain an

individualís usual level of BP outside the clinic setting and

thereby identify individuals with WCH. In addition to

detection of WCH, ABP devices may be used to identify

individuals with a nondipping BP pattern and to evaluate

apparent drug resistance, hypotensive symptoms to

medications, episodic hypertension, and autonomic

dysfunction. Use of ABP monitoring has been controversial.

First, few prospective studies have determined whether this

technology predicts cardiovascular disease outcomes and

whether this technology provides additional information

beyond that of routine clinic measurements. Second, insurers

have been concerned that health care providers might

overutilize ABP. Third, it has been unclear whether SMBP

monitoring is a satisfactory and less expensive alternative to

ABP monitoring. Accordingly, health insurers have been

reluctant to reimburse for ABP monitoring. 

Reporting the Evidence

The utility of BP monitoring outside of the clinic setting was

a topic nominated to the Agency for Healthcare Research and

Quality (AHRQ) by a group of experts in BP measurement. In

September of 2000, the AHRQ awarded a contract to the

Johns Hopkins Evidence-based Practice Center (EPC) to

prepare an evidence report on this topic. The Johns Hopkins

EPC established a team and work plan to develop a report that

would identify and synthesize the best available evidence on BP

monitoring. One of the first tasks was the identification of an

appropriate partner. In December 2000, the National High

Blood Pressure Education Program (NHBPEP) of the National

Heart, Lung, and Blood Institute (NHLBI) of the National

Institutes of Health (NIH) hosted a working meeting. The

NHBPEP includes representatives from national professional

and voluntary organizations as well as from Federal agencies.

Arising from that meeting was an agreement from the

NHBPEP Coordinating Committee to partner with the Johns

Hopkins EPC on this project.

A core group of five clinically and/or methodologically

oriented technical experts advised the EPC team at key points

in the project. This group included experts in ABP

monitoring, SMBP monitoring, clinic BP measurement,

clinical hypertension, and diagnostic test evaluation. These

individuals reviewed draft research questions. Also, this core

group along with additional experts in BP measurement and

hypertension provided early input at an ad hoc meeting

convened by the NHBPEP. The target population consisted of

nonpregnant adults with BP in the nonhypertensive or

hypertensive range. These individuals are candidates for BP

monitoring, and many are candidates for anti-hypertensive

drug therapy.

Key Questions

After an extensive deliberative process and with input from

the technical experts, the following questions were developed:

• Comparison of clinic, ambulatory, and SMBP readings. 

1a. What is the distribution of the BP differences

between clinic, ambulatory, and SMBP readings? If

there are differences, are these differences

reproducible?

1b. What is the prevalence of WCH as defined by

SMBP? Is this pattern reproducible?

1c. What is the prevalence of WCH as defined by ABP

measurement? Is this pattern reproducible?

• SMBP levels and WCH based on SMBP as related to

clinical outcomes.

2a. Is SMBP more or less strongly associated with BPrelated target organ damage than clinic BP

measurements?

2b. Does SMBP predict subsequent clinical outcomes?

2c. What is the incremental gain in prediction of clinical

outcomes from use of self-measurement devices

beyond prediction from clinic BP alone?

2d. What is the effect of treatment guided by SMBP in

comparison to treatment guided by clinic BP, in

terms of:

i. BP-related target organ damage

ii. symptoms

iii. use of anti-hypertensive drug therapy

iv. BP control

• ABP levels and WCH based on ABP as related to clinical

outcomes

3a. Is ambulatory blood pressure more or less strongly

associated with BP-related target organ damage than

clinic BP measurements?

3b. Does ambulatory blood pressure predict subsequent

clinical outcomes?

3c. What is the incremental gain in prediction of clinical

outcomes from use of ambulatory devices beyond

prediction from clinic BP alone?

3d. What is the effect of treatment guided by ABP in

comparison to treatment guided by clinic BP, in

terms of:

i. BP-related target organ damage

ii. symptoms

iii. use of anti-hypertensive drug therapy

iv. BP control

3
• Does the evidence for the above questions vary according

to a patient’s age, gender, income level, race/ethnicity, and

clinical subgroups (e.g., hypertensive/normotensive,

diabetic, renal transplant status)?

Methodology

Searching the literature included identifying reference

sources, formulating a search strategy for each source, and

executing and documenting each search. A comprehensive

search plan was developed that include electronic and hand

searching. Several electronic databases were searched and a

separate strategy was developed for each. First searched was

MEDLINE®, which was accessed through PubMed®. Searches

using PubMed® were completed in January 2001 and March

2001. The Cochrane CENTRAL Register of Controlled Trials

was searched once (Issue 1, 2001). HealthSTAR was searched

in February 2001.

Hand searching for possibly relevant citations took several

forms. First, priority journals were identified through an

analysis of the frequency of citations per journal in the database

of search results as well as through discussions amongst the

EPC team. Fifteen specialty and general journals were

identified. The January to May 2001 issues of these journals

were searched. For the second form of hand searching, a

database of reference material, identified through an electronic

search for relevant guidelines and reviews, through discussions

with experts, and through the article review process, was

created in the reference management software, ProCite. A

listing of titles and abstracts from this database, the BP

References Database, was reviewed by the principal investigator

to identify key articles. The reference lists of these articles were

then reviewed to identify possibly relevant citations. Finally,

proceedings from recent conferences were also reviewed.

Abstract and Article Review Process

Specific inclusion and exclusion criteria were applied at each

of three levels of review (two levels of abstract review, then

article review). Inclusion criteria became more stringent at each

level. The titles and abstracts were reviewed for each article

identified. During the abstract review process, emphasis was

placed on identifying all articles that may possibly have original

data pertinent to the questions. For the first-level abstract

review, titles and abstracts for all articles retrieved by the

literature search were printed on an abstract form and

distributed to two reviewers. Because of the extensive volume of

literature, a second level abstract review, at which additional

exclusion criteria were applied, was necessary. Citations deemed

eligible for full article review based on the initial abstract review

were printed onto the second level abstract form and

distributed to two reviewers.

The purpose of the article review was to confirm the

relevance of each article to the research questions, to determine

methodological characteristics pertaining to study quality, and

to collect evidence that addressed the research questions.

Because of the large number of citations that remained eligible

for full article review even after the second level abstract review,

additional exclusion criteria were applied at the article review

level. The final full list of exclusion criteria differed by question.

For instance, for question 1a, a comparison of BP by the

different techniques, the criterion of more than 1 day of

measurement for clinic BP was added because an average clinic

BP based on just 1 day of measurements (typically just one to

three readings) is extremely imprecise and could lead to a biased

comparison with ABP or SMBP.

Article review forms were developed to collect data in a

standardized fashion. This process was complex and time

consuming due to the heterogeneity of the literature and the

diverse questions being addressed. These forms then guided

article review. For each of the articles deemed potentially

eligible after second-level abstract review, two reviewers read the

article, confirmed eligibility status, abstracted key information,

and assessed study quality on several dimensions. Because of

heterogeneity in study design, data collection forms and

elements differed by research question.

Presentation of Results

Evidence tables that summarize aspects of study quality,

characteristics of the study population, and features of BP

measurement were constructed. For most research questions,

these summary tables were similar. However, the evidence

tables that display study results differed substantially by research

question. Qualitative summaries were prepared which

synthesized the evidence and included, to a limited extent, a

quantitative assessment (for example, the number/percent of

studies with significant associations, overall and occasionally by

relevant study characteristics). A draft version of the report was

distributed to the partner, the technical advisory group, and

other peer reviewers. All substantive comments were collated,

the responses of the EPC team summarized, and edits were

made to the report as appropriate.

Findings

Key question 1. Comparison of clinic BP, SMBP, and

ABP readings.

• Question 1a. Distribution of BP differences. 

A total of 18 studies addressed the distribution of BP

differences. BP levels measured outside the clinic

setting differed from those obtained in the clinic.

For both systolic and diastolic BP, clinic

measurements exceeded SMBP, daytime ABP,

4
nighttime ABP, and 24-hour ABP. In the few studies

that compared SMBP and ABP, daytime ABP and

SMBP appeared similar, while nighttime ABP was

consistently lower than SMBP. The literature was

insufficient to determine whether these BP

differences are reproducible.

• Question 1b. Prevalence of WCH based on SMBP.

A total of four studies addressed this issue. Hence,

the literature was insufficient to determine the

prevalence of WCH by SMBP. 

• Question 1c. Prevalence of WCH based on ABP. 

A total of 16 studies addressed this issue. Prevalence

varied by WCH definition and study population.

Overall, the prevalence was approximately 20 percent

among patients with hypertension. Only two studies

addressed the reproducibility of WCH. Hence, the

literature was insufficient to determine whether

WCH based on ABP is reproducible.

Key question 2. The relationship of SMBP levels and

WCH based on SMBP to clinical outcomes.

• Question 2a. Associations of SMBP with target organ

damage. 

Only one study addressed this issue. Hence, the

literature was insufficient to determine the

associations of absolute SMBP levels or WCH as

determined by SMBP with left ventricular mass or

proteinuria.

• Question 2b. Associations of SMBP with clinical

outcomes in prospective studies.

Only one study addressed this issue. Hence, the

literature was insufficient to determine whether

absolute SMBP levels or WCH based on SMBP

predicts subsequent CVD. 

• Question 2c. Comparison of risk prediction from

SMBP and clinic BP.

Only one study addressed this issue. The dearth of

studies combined with the poor or uncertain quality

of clinic BP measurements precluded an answer to

this question.

• Question 2d. Effect of treatment guided by SMBP. 

Twelve trials addressed this issue, but the evidence

was inconsistent. In half of these trials, interventions

that included SMBP led to reduced BP. Two trials

used contemporary SMBP technology which can

store and synthesize SMBP measurements and which

can generate BP reports. In both of these trials, the

SMBP intervention led to reduced BP.

Key question 3. The relationship of ABP levels and

WCH based on ABP to clinical outcomes.

• Question 3a. Cross-sectional associations of ABP with

target organ damage.

A total of 25 studies addressed these issues. Left

ventricular mass and albuminuria were positively

associated with ABP. 

• Question 3b. Associations of ABP with clinical events in

prospective studies.

A total of 10 studies addressed this issue. In each

study, at least one dimension of ABP predicted

subsequent clinical events, primarily CVD. In two

of these studies, WCH was associated with a reduced

risk of CVD relative to the risk associated with

sustained hypertension. No prospective study

adequately compared the risk associated with WCH

relative to the risk associated with non-hypertension.

In four of five studies, a nondipping or inverse

dipping pattern predicted an increased risk of adverse

events.

• Question 3c. Comparison of risk prediction from ABP

and clinic BP.

A total of nine prospective studies addressed this

issue, but only two studies assessed incremental gain,

that is, whether ABP provided additional

information that was predictive of risk beyond that

of clinic BP. However, the poor or uncertain quality

of clinic BP measurements precluded a satisfactory

comparison of risk prediction from ABP and clinic

BP.

• Question 3d. Effect of treatment guided by ABP.

Only two trials addressed this issue. Hence, the

literature was insufficient to determine the effects of

treatment guided by ABP. 

Key question 4. Findings according to subgroups.

• The vast majority of studies included both men and

women, but few studies reported results separately by

gender. 

• Few studies reported enrollment of AfricanAmericans, and race-stratified data were rarely

presented. 

• The only notable subgroup finding was a higher

prevalence of WCH in women than in men.

In summary, ABP levels and ABP patterns were associated

with BP-related target organ damage in cross-sectional studies.

Likewise, in prospective studies, higher ABP, sustained

hypertension, and a nondipping ABP pattern were associated

with an increased risk of subsequent CVD events. Few studies

examined corresponding relationships for SMBP. An

5
inadequate number of clinic BP measurements, as well as the

poor or uncertain quality of clinic BP measurements, precluded

satisfactory comparisons of risk prediction based on ABP or

SMBP with risk prediction based on clinic BP. In aggregate,

these findings provide some support for use of ABP monitoring

in evaluating prognosis. However, evidence was insufficient to

determine whether the risks associated with WCH are

sufficiently low to consider withholding drug therapy in this

large subgroup of hypertensive patients. For SMBP, available

evidence from several trials suggested that use of SMBP can

improve BP control; however, further trials that evaluate

contemporary SMBP devices are needed.

Future Research

The optimal approach to measure BP remains uncertain. In

view of the high prevalence of uncontrolled hypertension, the

continuing epidemic of BP-related diseases, and the potential

for alternative measurement techniques to improve diagnosis

and target therapy, there is a need for comparative studies that

assess the relative efficacy, feasibility, and costs of ABP,

contemporary SMBP technology, and clinic BP. Specific types

of research needs are as follows:

• Prospective observational studies that include SMBP,

ABP, and clinic BP. Specific research questions include: 

• What is the repeatability of WCH?

• What are the risks associated with WCH? In

particular, is the risk associated with WCH

sufficiently low to justify non-treatment? If yes, in

which patients?

• Does WCH as assessed by SMBP carry the same risk

as WCH as assessed by ABP?

• What are the risks associated with nondipping status?

• Is nondipping status a surrogate for some other

variable that might be measured more easily, that is,

without ABP? 

• What is the incremental gain from use of SMBP or

ABP over clinic BP alone? 

• Clinical trials that test whether contemporary SMBP

technology, compared to conventional management by

clinic BP, can improve BP control and health outcomes.

An additional comparison group might include BP

management by ABP. These trials should also compare

the aggregate costs of these approaches. 

• Decision analyses that determine the costs and effects of

strategies that integrate clinic BP, SMBP, and ABP. 

• Synthesis of evidence on BP measurements in clinic

setting, including issues related to the accuracy and

performance of different devices (mercury, aneroid,

automated BP) and different observers (physicians,

nurses, technicians).

In future research, clinic BP should be measured

appropriately by trained observers using validated equipment;

measurements should be obtained at several visits. Also,

because of the dearth of large-scale, high-quality studies, there

is a clear need for government sponsorship of key studies.

To improve the quality of ABP and SMBP publications,

standardized methods should be disseminated to researchers

and authors. Also, journals should require standardized

approaches for presenting ABP data. For published articles, full

copies of protocols should be made available, perhaps on the

Web. This is especially important because the intense pressure

from editors to shorten manuscripts typically leads to

reductions in the methods section.

Availability of the Full Report

The full evidence report from which this summary was taken

was prepared for the Agency for Healthcare Research and

Quality (AHRQ) by the Johns Hopkins Evidence-based

Practice Center (EPC), Baltimore, MD, under contract

number 290-97-006. It is expected to be available in fall 2002.

At that time, printed copies may be obtained free of charge

from the AHRQ Publications Clearinghouse by calling 800-

358-9295. Requesters should ask for Evidence

Report/Technology Assessment No. 63, Utility of Blood Pressure

Monitoring Outside of the Clinic Setting. In addition, Internet

users will be able to access the report and this summary online

www.ahrq.gov

AHRQ Pub. No. 03-E003

November 2002 

ISSN 1530-4396