Out-of-office blood pressure readings help predict CVD risk

Dec 21 2004

Blood pressure readings taken at home with approved devices can be a useful addition to blood pressure management, and may even predict cardiovascular disease (CVD) risk better than readings from the doctor’s office alone, according to a scientific statement issued today by the American Heart Association.

The Recommendations for Blood Pressure Measurement in Humans, published in Hypertension: Journal of the American Heart Association, is an update of 1993 guidelines on blood pressure measurement. While the new emphasis on out-of-office readings is the most significant change, the recommendations also emphasize using the proper cuff size when measuring blood pressure.

The most common error in measuring blood pressure in the outpatient setting is mis-cuffing, the statement says. Most mis-cuffing involves using a cuff too small for someone with large arms. Using small cuffs for children and small adults is also important.

“Since the last statement, there have been huge changes in the technology used to measure blood pressure and in our knowledge about the significance of different measurements,” said lead author Thomas G. Pickering, M.D., D.Phil., director of the Behavioral Cardiovascular Health and Hypertension Program at Columbia University Medical Center in New York.

“We’ve found that blood pressure measurements taken by doctors in their offices may actually be unreliable in many patients. For that reason, there is wider acceptance of blood pressure readings taken by patients in their homes, and of 24-hour ambulatory blood pressure monitoring.”

If there is a discrepancy between an out-of-office measurement and the office measurement, “physicians should consider the importance of the out-of-office readings if the measurement was taken in a reliable way,” Pickering said.

Ambulatory blood pressure monitoring measures blood pressure at regular intervals around the clock, while the person does normal activities and keeps an activity diary that can be compared with the measurements.

Ambulatory monitoring can also identify people with hypertension whose blood pressure stays high throughout the night, when normal levels are about 15 millimeters of mercury (mmHg) lower than during the day. Increasing evidence shows that blood pressure that does not dip at night may be associated with higher cardiovascular risk, according to the statement.

“The 1993 document didn’t say much about home and ambulatory monitoring, but now there is much more emphasis on out-of-office measurements and less exclusive reliance on traditional methods of measurement,” Pickering said. Emphasizing out-of-office blood pressure measurement does not mean that your doctor will no longer check your blood pressure, he said.

The statement encourages patients to monitor their blood pressure at home, using validated devices and providing the readings to their physicians to use as supplemental information in monitoring treatment.

National data published last summer indicated that at least 65 million Americans — or almost one-third of adults — have high blood pressure. High blood pressure is defined as consistent systolic pressure of 140 mm Hg or higher, or diastolic pressure of 90 mm Hg or greater, taking hypertensive medicine, or being told at least twice by a healthcare provider that a person has high blood pressure. Systolic pressure is the top number and diastolic is the bottom number in a blood pressure reading. High blood pressure is a major risk factor for coronary heart disease, stroke and kidney failure. It is usually symptomless and is often called a “silent killer.”

Millions of adults with blood pressure levels between 120–139 mm Hg systolic and 80–89 mm Hg diastolic are considered to have “prehypertension.” People with prehypertension may have a higher cardiovascular risk. They should institute lifestyle changes to lower their blood pressure and be followed closely by a healthcare provider to ensure proper treatment in case high blood pressure develops.

“This makes it extremely important to accurately detect small differences in blood pressure,” Pickering said.

The preferred device for measuring blood pressure in the medical setting is still a mercury sphygmomanometer, but these devices are being phased out, partially because of environmental concerns about mercury contamination, he said.

“However, alternative devices can become inaccurate, so calibration with a mercury reading is critical to ensuring accuracy,” he said.

Blood pressure can vary significantly depending on the conditions under which it is measured in the hospital or doctor’s office. Ideally, blood pressure should be taken after several minutes’ relaxation, when a person is seated comfortably in a chair, legs uncrossed, not talking, back and arm supported, and the cuff placed on bare skin.

Co-authors are John E. Hall, Ph.D.; Lawrence J. Appel, M.D.; Bonita E. Falkner, M.D.; John Graves, M.D.; Martha N. Hill, Ph.D.; Daniel W. Jones, M.D.; Theodore Kurtz, M.D.; Sheldon G. Sheps, M.D.; and Edward J. Roccella, Ph.D., M.P.H.