Blood pressure readings often unreliable

While assessment increasingly occurs outside the office, efforts continue to improve clinician determination of the readings.

By — Posted June 11, 2007

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The measurement of blood pressure during a doctor visit is fraught with problems that can lead to some cases of hypertension being overlooked or some patients being misclassified as having the condition. That was the message of several presentations at last month's American Society of Hypertension 22nd annual scientific meeting, held in Chicago.

"Of all the procedures done in a doctor's office, measurement of blood pressure is usually the least well performed but has the most important implications for the care of the patient," said Norman M. Kaplan, MD, clinical professor of internal medicine at the University of Texas Southwestern Medical Center, who moderated one of the sessions.

Experts said the in-office assessment is unreliable because blood pressure can be raised or lowered by the presence of the medical professional taking it. The numbers also can be different from one arm to the other or from one minute to the next.

The American Heart Assn. guidelines -- which call for blood pressure to be measured at least five minutes after a patient arrives in the office while he or she is sitting in a chair with the arm supported -- often are not followed. This strategy also can miss patients whose blood pressure peaks at night, first thing in the morning or otherwise out of the office setting, and thus miss patients who might need to lower blood pressure.

"There are so many problems trying to quantify this measurement because it's so variable, and the whitecoat effect is a big problem," said Thomas Pickering, MD, DPhil, director of the behavioral cardiovascular health and hypertension program at Columbia University College of Physicians and Surgeons in New York. "Somehow we assume that these readings have some relevance to what's going on between visits."

One study presented at the meeting said patients treated for hypertension whose blood pressure either did not fall while they were sleeping or made an extreme dip during this time were at a much higher risk for cardiovascular events than were those who had a normal nighttime decrease.

"This study underscores the need for nighttime blood pressure monitoring of hypertensive patients," said Dr. Sante D. Pierdomenico, lead author and professor of medicine and aging science at the University of G. d'Annunzio in Chieti, Italy.

Experts would like to see multiple readings taken in the office before any decisions are made regarding initiating or changing treatment. They also predict a jump in reliance on multiple daily readings taken by the patient with at-home devices.

Technical improvements in these private-use instruments mean they can be as accurate as ambulatory monitoring, which is regarded as the best way to assess blood pressure. These suggestions are in line with AHA guidelines that call for more emphasis on out-of-office readings.

"In the future, blood pressure monitoring will be centered in the home and not in the physician's office," said Dr. Pickering, who also was the lead author of the guidelines.

Implications of the shift

This shift has the potential for more engagement on the part of the patient in getting his or her blood pressure under control.

"At-home monitoring clearly empowers patients to do what they need to do and makes them more involved in their care," said William B. White, MD, professor of medicine and chief of the section of hypertension and clinical pharmacology at the University of Connecticut School of Medicine.

Even so, experts don't believe the well-ensconced practice of in-office blood pressure measurement will go away completely, particularly since ambulatory measurement has its own challenges of cost and convenience. Some of the at-home monitors on the market also lack reliability and validation, experts noted.

But because in-office measurement is still viewed as having some utility, great concern surrounds the phase-out of sphygmomanometers containing mercury. Mercury-based equipment is being eliminated because of environmental risks related to disposal. Those opposed to the phase-out say the risk from the mercury in these machines is minimal and accuracy is unparalleled. Quality controls for such tools overall are minimal, while mercury-free versions often require more effort to calibrate and maintain.

"We need to be sure that blood pressure measurement in this day of complexity is as reliable as a glucose monitor or measuring cholesterol," said Daniel W. Jones, MD, professor of medicine at the University of Mississippi Medical Center. "And this will become more important as evidence accumulates for tight control. Continue to use [a sphygmomanometer with] mercury if it's available."

Multiple readings one approach

Research also indicates that it may be possible to make the in-office measurement of blood pressure more accurate.

One study suggested the white-coat effect could be detected through multiple in-office readings taken using the correct cuff size and with the arm supported at the level of the heart. Researchers suggest that this approach could reduce the number of people unnecessarily recommended for ambulatory monitoring.

"Ambulatory monitoring is considered the gold standard, but it's impractical for routine patient management," said David P. Fuschetto, MD, lead author of the paper and a second-year resident at North Shore-Long Island Jewish Health System in New York.

Meanwhile, research that was conducted at Guglielmo da Saliceto Hospital in Piacenza, Italy, assessed the possibility of measuring a patient's blood pressure with a device set to automatically take a reading every 2.5 minutes. The patient was left alone, to minimize the white-coat effect, and the final six readings out of 10 were averaged. Researchers found that this achieved results comparable with ambulatory monitoring.

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How accurate is that BP reading?

  • The presence of a health care professional can raise or lower blood pressure.
  • The numbers can be different between arms.
  • Immediate events, such as a lack of sleep or stress, can temporarily increase it.
  • Problematically high blood pressure may occur at night, early in the morning, or at other times when the patient is not in the clinic.

Source: American Society of Hypertension 22nd Annual Scientific Meeting and Exposition, Chicago, May 19-22

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