How to measure blood pressure correctly

Here's how some common mistakes look.

“Blood pressure is measured incorrectly about half the time,” says physician William B. White, editor of the medical journal Blood Pressure Monitoring.

Here are some common mistakes that can cause your systolic blood pressure reading to be off by 2 to 20 points. If you have hypertension, the error is more likely to be at the higher end.

Your doctor should take your blood pressure at least twice on at least two separate occasions before diagnosing hypertension.

Posture. Sitting on an exam table or a chair with no back support can raise your diastolic pressure.¹ (That’s the lower number.)

Arm Position. Your upper arm should be supported at heart level by the person taking your blood pressure, not by you. Your pressure is higher if your arm rests below your heart level, and is lower if your arm rests above your heart.²

Feet Position. If your feet aren’t flat on the floor or your legs are dangling or crossed, your blood pressure reading may be higher.³

Talking. Even a casual conversation can raise your pressure.⁴

Miscuffing. Wrapping the cuff around clothing can lead to a higher reading. So can a cuff that’s too tight (too small for your arm or wrapped too tightly). And a cuff that’s too loose or too large can lead to lower readings.⁵

Caffeine. Consuming caffeine 30 minutes to two hours before the measurement can raise your pressure.⁶

Cigarettes. Smoking within half an hour of the measurement can increase blood pressure.⁷

Bladder. A (very) full bladder can raise your pressure.⁸

Exercise. Aerobic exercise within 30 minutes of the measurement can lower your pressure.^9,10

Checking Pressure at Home

“You want to make sure that the device you use was independently assessed and validated,” says Blood Pressure Monitoring editor William B. White. The American Heart Association recommends an automatic, cuff-style, bicep (upper-arm) monitor. You should be able to find one for $50 to $100. Wrist and finger monitors give less reliable readings, says the AHA. For a list of validated monitors, see dableducational.org/sphygmomanometers/recommended_cat.html or Consumer Reports, which rated monitors in May 2015.

Tip: To verify your monitor’s accuracy and that you’re using it properly, take it with you to your next doctor’s appointment.

¹Am. J. Hypertens. 3: 240, 1990.
²Circulation 111: 697, 2005.
³Blood Press. Monit. 4: 97, 1999.
⁴Arch. Psych. Nurs. 6: 306, 1992.
⁵Epidemiology 2: 214, 1991.
⁶Ann. Pharmacother. 42*: 105, 2008.
⁷N. Eng. J. Med. 295: 573, 1976.
⁸Hypertension 14: 511, 1989.
⁹Clinics 65: 317, 2010.
¹⁰J. Hum. Kinet. 43: 49, 2014.