Clinic-Based BP Measurement Is Inaccurate for Diagnosing Hypertension

Compared with ambulatory blood pressure measurements, those obtained in the clinic or at home are far less accurate.

Most clinicians rely on clinic- or home-based measurement of blood pressure (BP) for diagnosing hypertension. However, whether such measurements are accurate is unclear. In this systematic review and meta-analysis of 20 studies that involved 5700 patients, U.K. investigators determined how accurately clinic- and home-based BP measurements diagnosed hypertension; daytime ambulatory BP measurements were the reference standard.

The studies varied in the number of BP measurements obtained for ambulatory (24–111), clinic (2–18), and home (18–56) monitoring. Compared with a mean daytime ambulatory BP of >135/85 mm Hg for diagnosing hypertension (the reference standard), a mean clinic BP of >140/90 had a sensitivity of 75% and a specificity of 75%, and a mean home BP of >135/85 had a sensitivity of 86% and a specificity of 62%. How often these differences affected clinical accuracy depended on the prevalence of hypertension: If prevalence was 10% (e.g., in people 40), only one in four diagnoses of hypertension based on clinic BP measurements would be correct, whereas, if prevalence was 50% (e.g., in people 65), then three in four diagnoses of hypertension would be correct.

Comment: These results have important implications: Many people with diagnosed hypertension are not really hypertensive, especially if the diagnoses were based on clinic BP measurements (i.e., white-coat hypertension). The study investigators suggest using clinic- or home-based BP measurements to screen for hypertension, followed by ambulatory BP measurement to diagnose hypertension so that unnecessary antihypertensive treatment can be avoided. Notably, Medicare reimburses for 24-hour ambulatory BP measurements only in patients with white-coat hypertension (ICD-9 code 796.2).

— Paul S. Mueller, MD, MPH, FACP

Published in Journal Watch General Medicine August 11, 2011

Citation(s):

Hodgkinson J et al. Relative effectiveness of clinic and home blood pressure monitoring compared with ambulatory blood pressure monitoring in diagnosis of hypertension: Systematic review. BMJ 2011 Jun 24; 342:d3621. (http://dx.doi.org/10.1136/bmj.d3621)

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