Averaged home blood pressure readings are more accurate

As few as five averaged home blood pressure readings could more accurately assess hypertension control than those taken in the office, researchers suggest.

To compare strategies for home or clinic blood pressure measurement, researchers conducted a secondary analysis of the Hypertension Intervention Nurse Telemedicine Study. A subset of 444 veterans with long-standing hypertension was followed for 18 months in primary care clinics affiliated with the Durham Veterans Affairs Medical Center. The sample was 92% men, about half of whom were black, with a mean age of 64 years who had been selected on the basis of previous poor blood pressure control. Three-quarters of them had had hypertension for at least 10 years. Study results appeared in the June 21 Annals of Internal Medicine.

In the study, blood pressure was measured repeatedly by using three methods: research blood pressure measurements at 6-month intervals, clinic blood pressure measurements obtained at varying intervals during outpatient visits, and home blood pressure measurements taken at least three times a week using a digital home monitor and telemedicine device.

Patients provided 111,181 systolic blood pressure measurements (3,218 research, 7,121 clinic, and 100,842 home measurements) over 18 months. Systolic blood pressure control rates at baseline (mean systolic blood pressure <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.

In the clinic, no single systolic blood pressure measurement from 120 mm Hg to 157 mm Hg allowed correct classification of a patient's blood pressure control with 80% or greater certainty. For systolic blood pressure measurements from 136 mm Hg to 144 mm Hg, at least 10 measurements are required before a patient can be correctly classified with at least 80% probability.

Results for home blood pressure measurements are similar to clinic results. For a single observed measurement, only readings of 123 mm Hg or less or 153 mm Hg or more could be correctly classified as in or out of control with at least 80% probability. Most observed mean systolic blood pressures could be accurately categorized with 80% probability based on the mean of five home measurements.

The results support reimbursement for home blood pressure monitoring, the authors suggested. “Current decisions about medication therapy are often made on the basis of one or two clinic measurements; these data suggest that this could be substantially improved for patients with a history of elevated blood pressure measurements when decisions are based on the average of several measurements, regardless of the setting,” they wrote.

An editorial pointed out that the American Heart Association called for blood pressure guidelines in 1939, but that clinical adoption has lagged and poor practices still include such habits as taking blood pressure readings through clothing. “The importance of accurate and precise [blood pressure] measurement has largely been ignored,” the editorialists wrote. “Given persistent problems in obtaining such measurements, a regulatory approach should be considered in which the Joint Commission, the National Committee for Quality Assurance, and other organizations set standards and monitor compliance. It is time to get serious about BP measurement.”

A patient summary is available online.