# Presentation: 337907

## TRANSLATING VISITS INTO PATIENTS USING AMBULATORY VISIT DATA 
(Hypertensive patient case study)

by Esther Hing, M.P.H. and Julia Holmes, Ph.D

**(Hypertensive patient case study)**
**by Esther Hing, M.P.H. and Julia Holmes, Ph.D**

## Outline of talk

- Source of data
- Two hypertension definitions compared
- Methodology translating visit to patients
- Accuracy of estimates assessed
- Example of analytic use of patient estimates

## Sources of data

- Split-panel study of 2001 NAMCS  and Outpatient Department (OPD) component of 2001 NHAMCS
- Study tested effects of form length on response rates and reporting levels
- Half of sample randomly assigned short form
- Half of sample randomly assigned longer form
- Data for each half sample weighted to reflect estimates for the nation.
- Data across both half samples also weighted to reflect national estimates

## Estimating hypertensive patients 18 years and older

- Visits limited to selected specialties and clinics where hypertensive patients more likely to be treated and to avoid multiple visits to different providers by same patient:
- cardiologists, primary care physicians (family or general practice, internal medicine, pediatrics, obstetrics and gynecology).
- selected hospital OPD clinics (general medicine, pediatric, obstetrics and gynecology).

## Hypertension definitions

|  | Full sample estimate | Half sample estimate |
| --- | --- | --- |
| Diagnoses  | X | X |
| Reason for visit | X | X |
| Hypertension check box |  | X |

## Number of adult visits with hypertension indicated by type of estimate: 2001 NAMCS/NHAMCS

## Methodology for translating visits to patients

- Information on past visits only collected for established patients previously seen by physician in office practice or hospital OPD

## Full sample distribution of visits to physician offices and hospital OPDs made by hypertensive adults during past 12 months: 2001 NAMCS/NHAMCS

## Assumptions

- Current visit assumed to be the _only_ visit for new patients.
- Established patients with unknown number of visits during past 12 months were assumed to have same category of visits as most frequent category (4-6 visits).

## Distribution of visits by number of physician visits after re-assignment of new patients and established patients with unknown number of visits

## Translating visits to patients

- Visits by patients known to have multiple visits during past 12 months are re-weighted by dividing the sampling weight by the midpoint of number of visit of visit category; e.g., midpoint of 4-6 visits category is 5.
- Re-weighting assumes that characteristics of the sampled visit are similar to previous visits made by the  patient to this provider during the past 12 months.

## Full sample distribution of hypertensive visits and estimated patients by number of physician visits during past 12 months: 2001 NAMCS/NHAMCS

## Half sample distribution of hypertensive visits and estimated patients by number of physician visits during past 12 months: 2001 NAMCS and NHAMCS Split-panel study

## Estimated number of adults with diagnosed hypertension from NAMCS/NHAMCS and NHIS: United States, 2001

- NOTE: NHIS is the National Health Interview Survey

- Patient estimates derived from NAMCS/NHAMCS visit data differ from  household survey (NHIS) estimate because of:
- Respondent reporting differences
- Household survey estimate includes persons not seen by a physician during last 12 months
- Household respondents could report for providers outside of scope of NAMCS/NHAMCS
- Other reasons

## Example of how derived patient estimates can be used

- Percent of hypertensive patients receiving recommended (evidence-based) drug therapy
- Guideline: 6th Joint National Committee on Detection, Evaluation and Treatment of High Blood Pressure (JNC VI), 1997.
- Recommendations vary by presence or absence of co-morbidities:
- Essential hypertension without co-morbidities
- Hypertension and diabetes
- Hypertension and ischemic heart disease

## Anti-hypertensives used in this study

- Antihypertensive treatment defined as a prescription for the following therapeutic drug classes:
- Diuretic
- Beta blocker
- Calcium channel blocker
- Angiotensin-converting enzyme (ACE) inhibitor
- Other antihypertensive drugs
- Combination drugs were disaggregated and allocated to the applicable therapeutic drug class.

## Recommended first-line anti-hypertensives (JNC VI)

- Diuretics or beta blockers for patients with essential hypertension and no co-morbidities
- ACE inhibitors for hypertensive patients with diabetes
- Beta blockers for hypertensive patients with ischemic heart disease

## Half sample percent of adult hypertensive patients and visits prescribed first-line anti-hypertensives by presence or absence of selected co-morbidities:  2001NAMCS/NHAMCS Split-panel study

## Anti-hypertensive prescribing pattern

- Percent prescribed diuretics or beta blockers for hypertension without co-morbid diabetes or ischemic heart disease varies by definition used
- Full sample estimate defined by diagnoses and reason for visit was 40.8 percent
- Half sample defined by check box, diagnoses and reason for visit was 48 percent

## Comparison of percent of adults with essential hypertension prescribed first-line anti-hypertensive medications (diuretic or beta blockers) by survey

- MEPS=Medical Expenditures Panel Survey

## Conclusions

- Patient estimates vary by data items used to define patients
- Inclusion of the hypertension check box in the definition resulted in a 72 percent higher estimate of hypertensive patients (34.9 million) than the estimate defined by diagnoses or reason for visit (20.3 million)

## Conclusions

- The outcome variable (percent of patients with hypertension prescribed diuretics or beta blocker) also varied by definition of hypertensive patients
- Half sample estimate similar to estimate based on BCBSM administrative data

## Implications for Data Users

- Translation of visits to patients produced valid estimates in this case study, but users need to assess applicability of assumptions used for user’s research
- Two definitions of hypertensive patients presented
- Information on hypertension check box not released on the 2001 public use files (PUF) for NAMCS and OPD component of 2001 NHAMCS, but will be included in 2005 surveys
- Diagnoses and reason for visit always available in PUF files
- Users need to be aware of differences in estimates and outcome variables associated with varying definitions of patients

## Limitations

- Estimates of drug prescribing patterns may includes cases where first-line therapy was already tried and the medications recorded reflect a newer treatment
- Estimated number of patients are rough approximations and may overestimate if established patients visited multiple sample physicians or hospital OPDs during the past 12 months.