December 14, 2018
Blood Pressure: 6 Common Errors in Measuring It
Be Well

Blood Pressure: 6 Common Errors in Measuring It

by John Swartzberg, M.D.  

We recently discussed the revised official guidelines for blood pressure, which lowered the cutoff for hypertension from 140/90 to 130/80—as well as the debate that ensued about this change. Often lost in this discussion is that those numbers are based on the assumption that blood pressure readings are done properly and are accurate, which is often not the case outside of research settings.

“In clinics, proper measurement may be the exception . . . rather than the norm,” a recent release from the American Heart Association (AHA) stated. That’s hardly news. There is a standard way to measure blood pressure, based largely on AHA guidelines, but studies have found that, because of improper technique, real-world readings done in medical offices are usually off by at least a few points.

Such errors don’t matter if your blood pressure is far above the cutoff for hypertension, or if it is normal (below 120/80). But it could affect your treatment if you’re in the gray area in between. Here are six common errors that can lead to inaccurately elevated blood pressure readings, according to the AHA:

  1. Poor sitting posture: Slouching, crossing your legs, or having unsupported feet can add 6 to 10 points to your reading. You should sit in a chair with your back supported and feet flat on the floor or a footstool.
  2. Unsupported arm: If your arm is hanging or you have to hold it up, your numbers may rise as much as 10 points. Your forearm should be supported by the practitioner (or a counter or chairback) at heart level.
  3. Wrapping the cuff over clothing: This can add anywhere from 5 to 50 points to your reading. The cuff should be placed on a bare arm.
  4. A cuff that’s too small for your arm: This can add 2 to 10 points.
  5. Talking: This can also add as much as 10 points. Stay silent and still.
  6. Having a full bladder: This can add 10 to 15 points to your reading (this one surprised me). Empty your bladder beforehand.
Other pointers: Don’t exercise, consume caffeine, or smoke during the 30 minutes before testing (of course, you shouldn’t smoke, period). Ideally, you should wait five minutes in a quiet room beforehand.

Two measurements should be done at least one minute apart and the results averaged; the first reading is often misleadingly elevated, as a study in JAMA Internal Medicine in June 2018 confirmed. And blood pressure should be measured in both arms, at least at the initial visit, with the second arm tested at least five minutes later.

To raise awareness among health care providers about the importance of accurate measurement, the AHA and American Medical Association are encouraging them to enroll in a national program called Target: BP. The program will help providers identify and correct measurement errors, as well as offer guidance for creating appropriate treatment plans for patients with hypertension and for partnering with patients to enable ongoing self-management, including teaching them to measure their blood pressure accurately at home.

Meanwhile, talk with your health care provider about your blood pressure results and ask any questions you have about how the measurement is being done. Discuss lifestyle changes that can help keep yourblood pressure under control. If your reading is elevated, make sure you’re retested several times before any treatment decision is made. You may be advised to measure your blood pressure periodically at home.

Better yet is ambulatory testing, which calls for wearing a device that automatically measures blood pressure and stores the results every 20 to 30 minutes for 24 to 48 hours. Such “gold standard” monitoring is endorsed by the U.S. Preventive Services Task Force and many other expertgroups to confirm an elevated office reading, before drug therapy is started,in order to avoid unnecessary treatment. It can also rule out “white-coat hypertension,” which causes elevations only in a medical setting.