• Benjamin J Powers, Maren K Olsen, Valerie A Smith, Robert F Woolson, Hayden B Bosworth, and Eugene Z Oddone.
• Center for Health Services Research in Primary Care, Durham Veterans Affairs Medical Center, and Duke University, Durham, North Carolina 27705, USA. ben.powers@duke.edu
• Ann. Intern. Med. 2011 Jun 21;154(12):781-8, W-289-90.

BackgroundThe optimal setting and number of blood pressure (BP) measurements that should be used for clinical decision making and quality reporting are uncertain.ObjectiveTo compare strategies for home or clinic BP measurement and their effect on classifying patients as having BP that was in or out of control.DesignSecondary analysis of a randomized, controlled trial of strategies to improve hypertension management. (ClinicalTrials.gov registration number: NCT00237692)SettingPrimary care clinics affiliated with the Durham Veterans Affairs Medical Center.Patients444 veterans with hypertension followed for 18 months.MeasurementsBlood pressure was measured repeatedly by using 3 methods: standardized research BP measurements at 6-month intervals; clinic BP measurements obtained during outpatient visits; and home BP measurements using a monitor that transmitted measurements electronically.ResultsPatients provided 111,181 systolic BP (SBP) measurements (3218 research, 7121 clinic, and 100,842 home measurements) over 18 months. Systolic BP control rates at baseline (mean SBP<140 mm Hg for clinic or research measurement; <135 mm Hg for home measurement) varied substantially, with 28% classified as in control by clinic measurement, 47% by home measurement, and 68% by research measurement. Short-term variability was large and similar across all 3 methods of measurement, with a mean within-patient coefficient of variation of 10% (range, 1% to 24%). Patients could not be classified as having BP that was in or out of control with 80% certainty on the basis of a single clinic SBP measurement from 120 mm Hg to 157 mm Hg. The effect of within-patient variability could be greatly reduced by averaging several measurements, with most benefit accrued at 5 to 6 measurements.LimitationThe sample was mostly men with a long-standing history of hypertension and was selected on the basis of previous poor BP control.ConclusionPhysicians who want to have 80% or more certainty that they are correctly classifying patients' BP control should use the average of several measurements. Hypertension quality metrics based on a single clinic measurement potentially misclassify a large proportion of patients.Primary Funding SourceU.S. Department of Veterans Affairs Health Services Research and Development Service.

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