Averaging Multiple Blood Pressure Measurements May Provide Optimal Assessment for Veterans with Hypertension

BACKGROUND:
The ability to effectively treat high blood pressure (BP) is one of the greatest medical advances of the last century. It is widely believed that the harmful effects of elevated BP are primarily attributable to an individual’s average daily (or “true”) BP level, with particular emphasis on systolic blood pressure (SBP). However, an individual’s underlying true BP is not readily available at the point of care, and there is no consensus among clinical guidelines and quality reporting standards on the setting, timing, and total number of BP measurements that should be used for classifying patients and making treatment decisions. Moreover, BP is increasingly monitored by patients at home, with recent surveys reporting that about 43% of primary care patients with hypertension use home monitors. This study compared home, clinic, and research SBP measurements in Veterans with hypertension – and estimated the certainty with which an individual’s true BP can be determined. Using data from an 18-month randomized controlled trial of a nurse-administered telemedicine intervention for hypertension, investigators focused on 444 Veterans treated for hypertension at the Durham VAMC.

FINDINGS:

• Clinicians who want to be certain that they are correctly classifying patients’ blood pressure control should average multiple measurements. Hypertension quality metrics based on a single clinic measurement potentially misclassify a large proportion of patients.
• The relationship between mean clinic and home SBP varied substantially, e.g., 52% had a mean clinic SBP that was at least 10 mm Hg greater than their mean home SBP.
• The within-individual variance declined markedly with increasing number of measurements and the relationship was similar across all three modes of measurement, with little added value of additional readings beyond 4-6 observed SBP measurements for all three modes.
• The proportion of patients with their SBP in control within the first 30 days (<140 mm Hg for clinic or research measurement; <135 mm Hg for home measurement) differed between mode of measurement: 28% were in control based on clinic measurement; 47% based on home measurement; and 68% based on research measurement.

LIMITATIONS:

• This study only considered the underlying mean SBP, but other components of BP independently predict risk; e.g., diastolic BP, maximum SBP, and morning BP surge.
• These results apply to patients with treated hypertension and a history of elevated values; results may differ for those with a long history of excellent BP control

AUTHOR/FUNDING INFORMATION:
This study was funded by HSR&D (IIR 04-426). Dr. Powers also was supported by an HSR&D Career Development Award and Dr. Bosworth by an HSR&D Research Career Scientist Award. All authors are part of HSR&D’s Center for Health Services Research in Primary Care, Durham, NC.

Powers B, Olsen M, Smith V, Woolson R, Bosworth H, and Oddone E. Measuring Blood Pressure for Decision Making and Quality Reporting: Where and How Many Measures? Annals of Internal Medicine June 21, 2011;154(12):781-88.