Which Strategies Are Best for Measuring BP and Diagnosing Hypertension?
New data on how and when blood pressure readings are most accurate
Hypertension management decisions generally are based on blood pressure (BP) measurements obtained in the clinic. Recent studies have clarified approaches to measuring BP and diagnosing hypertension.
How many BP measurements should be made before hypertension is diagnosed? In a Veterans Affairs study, researchers compared three methods of BP measurement (outpatient clinic, home electronic device, and standardized research measurements) and showed that, regardless of method, averaging multiple BP measurements lowered within-patient variability; for diagnosing hypertension, a minimum of five or six measurements is necessary (JW Gen Med Jul 12 2011).
How accurate are manual BP measurements? In a study of manual BP measurement and automated electronic BP measurement, researchers found that automated BP measurement mitigated white-coat effects on BP and was more accurate than manual BP measurement; the standard for comparison was an ambulatory monitoring device that automatically measures BP every 15 to 30 minutes during a 24-hour period. Notably, automated BP measurements in this study were obtained using the BpTRU device; after positioning the BpTRU cuff, the patient is left alone, and the device automatically records five BP readings over 10 minutes and displays an average (JW Gen Med Feb 17 2011).
How accurate are clinic- and home-based BP measurements for diagnosing hypertension? A meta-analysis showed that a mean clinic BP of >140/90 mm Hg had a sensitivity of 75% and a specificity of 75% and that a mean home BP of >135/85 mm Hg had a sensitivity of 86% and a specificity of 62% for diagnosing hypertension (with ambulatory BP measurement as the gold standard). Clearly, clinic- and home-based BP measurements are not perfect tests for diagnosing hypertension. However, the higher the prevalence, the more accurate clinic- and home-based BP measurements are (JW Gen Med Aug 11 2011).
Is ambulatory BP measurement a cost-effective approach to diagnosing hypertension? Investigators compiled evidence-based assumptions regarding the sensitivity and specificity of clinic- and home-based BP measurements relative to ambulatory BP measurement, the prevalence of hypertension, and other data. Ambulatory BP measurement (compared with clinic or home measurement) was the most cost-effective strategy, mainly because it prevented misdiagnosis and unnecessary treatment (JW Gen Med Sep 8 2011).
What are the take-home points of these studies?
- One BP measurement is not enough for diagnosing hypertension several are better.
- Electronic BP measurement devices that record multiple readings over time (e.g., BpTRU) are more accurate and less susceptible to white-coat effects than are manual BP devices.
- Clinic- and home-based BP measurements can be accurate, if the prevalence of hypertension is high.
- Ambulatory BP measurement can be helpful when the diagnosis is unclear. (Notably, Medicare reimburses for 24-hour ambulatory BP measurement only in patients with white-coat hypertension ICD-9 code 796.2).
[Powers, et al study: Medline ® abstract | Free full-text Ann Intern Med article PDF]
[Myers, et al study: Medline ® abstract | Free full-text BMJ article PDF in PubMed ® Central]
[Hodgkinson, et al study: Medline ® abstract | Free full-text BMJ article PDF in PubMed ® Central]
[Lovibond, et al study: Medline ® abstract]
Paul S. Mueller, MD, MPH, FACP
Published in Journal Watch General Medicine December 29, 2011
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