Study Shows Differences in Blood Pressure Readings Taken at Home and in Doctors' Offices
By Salynn Boyles
WebMD Health News
Reviewed By Laura J. Martin, MD
June 20, 2011 -- The so-called "white coat effect" is both real and common in the management of hypertension and it may be a significant cause of patient overtreatment, a new study finds.
Researchers from Duke University and the Durham VA Medical Center report that blood pressure readings taken in doctors' offices were consistently higher than those taken at home or in the research setting.
Doctors largely rely on one or two blood pressure readings taken in their offices to determine if patients need treatment for high blood pressure or if hypertension is adequately controlled in patients who are already on medication.
The researchers concluded that repeated measurements taken at home may help give a more accurate picture of blood pressure control than a single reading in a doctor's office.
Duke assistant professor of medicine Benjamin J. Powers, MD, who led the research team, says the finding lends credence to the notion that the stress of a medical exam can cause large elevations in blood pressure.
"Blood pressure normally fluctuates from hour to hour, and from day to day" he tells WebMD. "Even knowing this, we were surprised to see how big the differences were between clinic and home readings."
Testing for High Blood Pressure
Close to one in three adults in the U.S. has high blood pressure, but only about half of these people are adequately controlling the condition with drugs, according to the CDC.
While undertreatment is far more common than overtreatment, the new research highlights the largely unrecognized risk of treating patients too aggressively based on falsely high blood pressure readings, Powers says.
The study included 444 male veterans being treated for hypertension who had blood pressure readings taken in three different settings: a doctor's office, at home with a blood pressure cuff; and in the research setting (which included multiple readings taken by a trained researcher).
Just one in three patients had either consistently controlled or uncontrolled blood pressure across all three settings over the 18-month study.
The researchers concluded that blood pressure needs to be tested five or six times to give the best estimate of the patient's true status.
Location of Blood Pressure Testing
The researchers also documented big differences between blood pressure readings taken in doctors' offices and the research setting.
A systolic blood pressure reading of 140 or above is considered high enough to warrant treatment, but many patients with a single reading in the 140 range may not really need to be on hypertension drugs, Powers says.
At the start of the study, the average systolic blood pressure measured in the clinical setting was 145, which was 15 higher than in the research setting.
In about half the study participants, systolic blood pressure readings were more than 10 higher in the doctor's office than in the research setting.
"This information makes the most difference for the patient with a blood pressure reading in the 140 ... range," Johns Hopkins Medical Center professor of medicine Lawrence J. Appel, MD, tells WebMD. "Multiple readings may be needed to determine if this patient really needs treatment."
In an editorial published with the study, Appel and colleagues called for guidelines to standardize blood pressure measurement in the clinical setting.
The study and editorial appear in the June 21 issue of the Annals of Internal Medicine.
Powers, B.J. Annals of Internal Medicine, June 21, 2011; vol 154: pp 781-788.
Benjamin J. Powers, MD, assistant professor of medicine, Duke University Medical Center and Durham Veteran's Administration.
Lawrence J. Appel, MD, MPH, professor of medicine; director, Welch Center for Prevention, Epidemiology and Clinical Research, Johns Hopkins University, Baltimore.
News release, Duke Medicine.
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