Like people, blood pressure cuffs come in many sizes. The American Heart Association (AHA) recommends that the length of the bladder that wraps around patients’ upper arms be 75 to 100 percent of their arm circumference for a snug but not excessively tight fit. Cuffs for a “regular” size adult might get accurate readings for a person with an arm circumference of around 27 to 34 inches, according to the AHA, but it would be inaccurate for somebody with a much smaller or larger size. Many previous studies have noted inaccurate blood pressure readings made with ill-fitting manual blood pressure cuffs that clinicians pump by hand to compress around the upper arm, but new research presented at the AHA’s Epidemiology, Prevention, Lifestyle & Cardiometabolic Health Conference 2022 suggests that inaccuracies also occur with newer, automated blood pressure monitors. “Accurate blood pressure measurement depends on proper patient preparation, positioning, measurement technique, and individualized selection of cuff size,” says Tammy Brady, MD, PhD, the lead author of the new study and the medical director of the pediatric hypertension program at Johns Hopkins University in Baltimore. Nearly half of U.S. adults have high blood pressure, according to the AHA. This is defined by the AHA as a systolic blood pressure (the “top number,” which measures the pressure blood exerts against artery walls when the heart beats) of at least 130 mmHg (millimeters of mercury), or a diastolic blood pressure (the “bottom number,” which measures the pressure blood exerts in the arteries when the heart rests between beats) of at least 80 mmHg. For the study, researchers compared blood pressure readings for 165 adults who had separate measurements done with both a “regular” adult-size cuff and with a cuff appropriately sized for their arm circumference. Overall, 30 percent of the study participants had hypertension, according to their systolic blood pressure. Slightly more than two in five people in the study had obesity. When these people who required an extra-large blood pressure cuff had measurements done with a “regular” adult size cuff, this inaccurately increased their systolic blood pressure readings by an average of 19.7 mmHg and their diastolic blood pressure readings by an average of 4.8 mmHg. In 39 percent of these cases, people with obesity were misdiagnosed with hypertension as a result. Similarly, people who needed a “small” blood pressure cuff had hypertension that went undetected in 22 percent of cases when their measurements were done with a “regular” adult size cuff. When these people who needed a smaller cuff had measurements with a “regular” cuff, this inaccurately decreased their systolic blood pressure readings by an average of 3.8 mmHg and their diastolic blood pressure readings by an average 1.5 mmHg. “The degree of under- or overestimation depends on the size discrepancy of the cuff to the size of the arm, and can be substantial,” says Jordana Cohen, MD, an assistant professor of medicine and epidemiology at the University of Pennsylvania Perelman School of Medicine in Philadelphia, who wasn’t involved in the new study. To avoid this problem and get your blood pressure checked with a cuff that fits, you should ask your provider to measure the circumference of the middle of your upper arm, Dr. Brady advises. You should also do this yourself before you buy a blood pressure monitor for home use. “If a cuff pops off when being inflated or if the device provides multiple error messages while you’re trying to obtain a blood pressure, that might be a sign the cuff is too small,” Brady says.
