One Size Doesn’t Fit All in Blood Pressure Measurement

Marcus A. Banks

August 07, 2023

As with porridge, so with blood pressure: Just right makes all the difference.

Ill-fitting blood pressure measurement cuffs produce erroneous readings that impair hypertension treatment, according to research published August 7 in JAMA Internal Medicine.

People whose mid-upper arm circumference exceeds 32 cm require larger cuffs than the standard size, but in many cases the regular-sized cuff is used on everyone. As a result, patients with larger arms may be falsely diagnosed with high blood pressure because of a too-small cuff, leading to overprescribing of medications that could make their health worse, according to the researchers.  

"A person whose blood pressure is 120/80, which is normal — if they’re using the wrong cuff, they could get a measurement that says 140/90, let’s say," said study author Tammy M. Brady, MD, PhD, vice chair for clinical research in the Department of Pediatrics in the Johns Hopkins University School of Medicine, Baltimore, Maryland. "They might think they not only have hypertension, but stage 2 hypertension. Providers might give one or even two medicines to lower this, which could lead to hypotension," Brady said.

Conversely, someone with smaller arms whose cuff is too big may present with an artificially low blood pressure. The implications of using ill-fitting cuffs are well known. Brady, among others, has studied the topic extensively. Even so, she said the measurement errors in the latest study were larger than expected.

The Goldilocks Test

People with an arm circumference of 20-25 cm should use a smaller cuff than the regular size, Brady and colleagues report. Circumferences of 25.1-32 cm require a regular-sized cuff; large cuffs are for circumferences of 32.1-40 cm; and extra-large cuffs should be used at 40.1-55 cm.

The study included 195 residents of Baltimore (128 women, 67 men; 132 Black, 58 White, 5 Hispanic) with an average age of 54 years. The researchers measured every participant’s blood pressure using an automated device on four occasions, taking three measurements each time.

The first three sets of measurements used, respectively, an appropriate cuff size for each person’s arm circumference; a cuff that was too big; and a cuff that was too small. This study design ensured that a regular-sized cuff would be used during one of the three measurements — sometimes that cuff was too small, sometimes it was appropriate, and other times it was too big.

The final set of three measurements used the appropriate cuff size for a person’s arm every time. Brady and colleagues then compared people’s blood pressure measurements when using the right-sized cuff to measurements with a regular-sized cuff that was not suited for them.

They found that using a cuff that was too large for the patient’s arm (ie, using a regular cuff when a small cuff was the right choice) led to understating systolic blood pressure by -3.6 mm Hg (95% CI, -5.6 to -1.7). A cuff that was one size too small — using regular instead of a large — overestimated systolic blood pressure by 4.8 (3.0-6.6) mm Hg. And a cuff that was two sizes too small — someone who should have received an extra-large cuff but received the regular size — overestimated systolic blood pressure by 19.5 (16.1-22.9) mm Hg. All differences were statistically significant, they reported.

"To our knowledge, this is the first randomized cross-over trial to examine the effect of miscuffing on automated blood pressure readings," wrote Mathias Lalika, MD, MPH, of the Mayo Clinic in Rochester, Minnesota; Stephen P. Juraschek, MD, PhD, of Beth Israel Deaconess Medical Center in Boston, Massachusetts; and LaPrincess C. Brewer, MD, MPH, of the Mayo Clinic in an editorial accompanying the journal article. "Interestingly, the degree of underestimation or overestimation increased as the appropriate cuff size progressed from the regular to extra-large BP cuff. More importantly, the effect of miscuffing did not vary with BP or obesity status."

"This was more of a pragmatic trial to see real world, all comers," Brady said, when regular-sized cuffs are used whether or not that made sense.

"This study reaffirms findings of previous studies and highlights a major source of error in blood pressure measurement," Raj Padwal, MD, director of the University of Alberta Hypertension Clinic, Edmonton, Alberta, Canada, told Medscape Medical News. Padwal, who was not involved in the study, said the findings highlight the importance of ensuring that technicians who typically measure blood pressure understand the value of using the right-sized cuff.

Brady noted that measuring arm circumference takes about 15 seconds. He advised health organizations and clinics to carry multiple cuffs sizes to avoid a scramble to find a right-sized cuff. In the editorial, Lalika, Juraschek, and Brewer call for particular attention to providing the right-sized cuffs to facilities that work with underserved populations, such as federally qualified health centers.

Padwal added that even a perfectly measured blood pressure test at a clinic indicates pressure at a moment in time. Ten minutes later the story could be different. For this reason, he and other clinicians recommend frequent home blood pressure measurements rather than relying solely on the sparse number of readings collected in the clinic setting.

"A properly educated patient can give many readings that are separated in space and time and, when averaged, can give a much better picture of overall blood pressure and future risk," Padwal said. 

Brady agreed with the value of home readings but said home-based readings also can be erroneous if the patient uses the wrong size of cuff. She co-chairs a committee for the American Medical Association that recommends validated home blood pressure measurement devices on a periodically updated website called Validate BP. The details for each device listing show the cuff sizes available per device. Many devices only provide the standard cuff, Brady noted, but some offer multiple cuff sizes.

"One of the things that would be great if it came out of this paper is if patients were empowered to ask physicians to measure their arm" and then use that information to select the appropriate cuff for their home device, she said.

Brady and Padwal report no relevant financial relationships.

This study was supported by Resolve to Save Lives. Resolve to Save Lives is funded by Bloomberg Philanthropies, the Bill & Melinda Gates Foundation, and Gates Philanthropy Partners, which is funded with support from the Chan Zuckerberg Foundation.

JAMA Intern Med. August 7, 2023. Abstract.

Marcus A. Banks, MA, is a journalist based in New York City who covers health news with a focus on new cancer research. His work appears in Medscape, Cancer Today, The Scientist, Gastroenterology & Endoscopy News, Slate, TCTMD, and Spectrum.

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