Can the wrong size blood pressure cuff affect reading?

Accurate and reliable blood pressure (BP) measurement is critical for the proper diagnosis and management of hypertension. So much so that a 5 mm Hg BP measurement error can lead to incorrect hypertension classification in 84 million individuals worldwide, according to a position statement published in the Journal of Hypertension. Understanding the ways BP measurement goes wrong, and how to tackle them, can improve diagnosis and management of hypertension.

The AMA has developed online tools and resources created using the latest evidence-based information to support physicians to help manage their patients’ high BP. These resources are available to all physicians and health systems as part of Target: BP™, a national initiative co-led by the AMA and American Heart Association.

Unfortunately, BP measurement is often suboptimally performed in clinical practice, which can lead to errors that inappropriately alter management decisions in 20% to 45% of cases. This inaccuracy has persisted despite extensive education and efforts to raise awareness on the adverse consequences of incorrect clinic BP measurement, according to the Lancet Commission on Hypertension Group position statement. That statement was co-written by AMA Vice President of Health Outcomes Michael Rakotz, MD, and Gregory D. Wozniak, PhD, who is director of outcomes analytics at the AMA.

“Many measurement errors can be minimized by appropriate patient preparation and standardized techniques. Validated semi-automated or automated upper arm cuff devices should be used instead of auscultation to simplify measurement and prevent observer error,” the position statement says.

The position statement cites multiple causes of inaccuracy in measurement. Here are four ways BP measurement goes wrong and how to address them.

There are instances in which the BP-measurement error is caused by the patient. Acute meal ingestion, caffeine or nicotine use can all negatively affect BP readings, leading to errors in measurement accuracy. If the patient has a full bladder, that can lead to an error in systolic BP of between 4 mm Hg and 33 mm Hg, compared with the white-coat effect can have an error of up to 26 mm Hg.

It is important for the patient to rest comfortably in a quiet environment for five minutes in a chair. The patient should also have an empty bladder and not have eaten, ingested caffeine, smoked or engaged in physical activity at least 30 minutes before the measurement.

Errors can also occur due to inaccuracies with the procedure. For example, having the patient’s arm lower than heart level can lead to an error of 4 mm Hg up to 23 mm Hg. Procedure related error might also occur if the patient’s legs are crossed at the knees or if the patient is allowed to talk during the BP measurement. A fast deflation rate also can harm accuracy.

If a cuff is too small or too large, errors in measurement can occur. Adding to inaccuracy is automated device variability, which can account for average error in systolic BP of between -4 mm Hg and -17 mm Hg.

“An important issue with automated devices is that many have not been clinically validated for measurement accuracy,” says the statement. “Clinical validation involves demonstrating that the device meets the accuracy requirements of international BP measurement standards.”

The process of clinical validation involves performing a protocol-based comparison using multiple measurements against blinded, two-observer auscultatory reference standard. For greater accuracy, only validated devices should be used.

One common error in the clinical setting is failure to include a five-minute rest period. Errors can also include talking during the measurement procedure, using an incorrect cuff size and failure to take multiple measurements.

Time constraints are also quite common for casual measurements. This is because a casual reading takes about two minutes to perform compared with eight minutes for a standardized measurement. Physician readings were also found to be higher than nurse readings, which is the white coat effect in action.

The physician, nurse or other health professional is responsible for performing proper BP measurement while ensuring—to the greatest extent possible—that all potential causes of inaccuracy are avoided.

Training programs can lead to short-term success in BP readings. These can be web-based or in-person. However, shorter web-based programs are preferred because of their practical advantages, lower cost and scalability.

Quality improvement programs that combine use of automated office BP measurement with physician and care team education on proper measurement, as well as advice on clinical workflow enhancement, can also improve readings.

Blood pressure cuffs really aren’t one-size-fits-all. To the contrary, a recent study suggests that people who get their blood pressure checked with a cuff that’s the wrong size for their arm circumference may have undetected hypertension or get incorrectly diagnosed with this condition.

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.

Can a tight blood pressure cuff cause a high reading?

Can size of blood pressure cuff affect reading?

What causes a false high blood pressure reading?

Can blood pressure cuff give false reading?