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Beware of the Single Blood Pressure
Abstract & Commentary
By Joseph E. Scherger, MD, MPH, Vice President, Primary Care, Eisenhower Medical Center, Clinical Professor, Keck School of Medicine, University of Southern California. Dr. Scherger reports no financial relationships relevant to this field of study.
Synopsis: Single blood pressure (BP) measurements are not reflective of the average BP 20% of the time. A series of BPs should be averaged for medical decision making. A series of home BP recordings is more accurate than those in the office for assessing the control of BP among hypertensive patients.
Source: Powers BJ, et al. Measuring blood pressure for decision making and quality reporting: Where and how many measures? Ann Intern Med 2011;154:781-788.
Hypertension is the most common chronic illness in adults and arguably the most important risk factor for coronary heart disease and stroke. Unlike other chronic diseases, hypertension has no laboratory measurement for diagnosis we rely on taking blood pressures (BPs).
BPs vary moment to moment and many factors can result in an abnormal reading, usually with higher values, such as the "white coat" effect, patients not being at rest, and poor technique. In the office, as patients come for preventive care and return visits, we are often in the situation of making medical decisions on their treatment based on one recording. Recent studies have shown that all patients with proven or suspected hypertension should obtain a series of BP recordings away from the medical office, referred to as ambulatory blood pressure monitoring, to guide medical decision making.1
This study done at the VA Medical Center associated with Duke University followed 444 veterans with hypertension, mostly men, over 18 months. A total of 111,181 BP measurements were obtained in three settings: the office, at home, and as part of the research protocol. All measurements were made using automated equipment. Each setting showed substantial variation in the results, such as a range between 120 and 157 in systolic BP. The patients "true" BP was calculated by taking the average BP over time. Regardless of setting, a single BP recording was considered inaccurate about 20% of the time.
Interestingly, the patients' BPs were considered under control 68% of the time in the research setting, 47% based on the home recordings, and only 28% based on the clinic measurements.
Measuring the quality of care in chronic disease is of vital importance in primary care. Compared with diabetes and hyperlipidemia, measuring outcomes in hypertension is fraught with error due to the unreliability of BP recordings. As shown in this study, our clinic recordings may be the worst for proper medical decision making.
All patients with known or suspected hypertension should have equipment at home for measuring BPs with training and evaluation of the equipment for accuracy. Medical decision making should be made by looking at a series of BPs over time and not on the single recording we obtain in the medical office. It is time for this practice to become axiomatic in primary care.
1. Wexler R. Ambulatory blood pressure monitoring in primary care. South Med J 2010;103:447-452.