Wrong BP Cuff Size May Lead to Wildly Inaccurate Readings

A cuff that is too snug or too loose on the mid-upper arm can lead to greatly exaggerated blood pressure measurements, results of a community-based study show.

“If you need a large adult cuff and you use a regular adult cuff, the blood pressure on average is overestimated by 5 millimeters of mercury systolic,” said Tammy M. Brady, MD, PhD (Johns Hopkins University, Baltimore, MD), who led the study. “But if you need an extra-large cuff and instead you're given a regular cuff that is two sizes too small, you can have a blood pressure measurement that's 20 millimeters of mercury higher than what your actual blood pressure is.”

Brady, who presented the findings yesterday in a poster session at the American Heart Association’s Epidemiology and Prevention | Lifestyle and Cardiometabolic Health (EPI|Lifestyle) Scientific Sessions 2022, told TCTMD that they highlight the potential for patient harm, especially if the incorrect measurements are acted upon by physicians.

“This has big implications, particularly for populations where there is significant overweight and obesity, because those are the people who tend to need those larger cuff sizes,” she added.

Pamela Lutsey, PhD, MPH (University of Minnesota, Minneapolis), co-chair of the EPI|Lifestyle program committee, told TCTMD that while the study is small, the results are compelling and speak to the importance of improving the quality of BP measurements.

“These data absolutely drive home the point that the wrong size blood pressure cuff can have serious consequences that are going to lead people to be managed inappropriately for their blood pressure,” she said. In 2019, the AHA issued an updated scientific statement on appropriate BP measurement that highlighted the steps necessary for accuracy, including proper cuff sizing and placement.

Undercuffing and Overcuffing

Brady and colleagues conducted the trial in 165 community-dwelling adults (mean age 55 years; 67% female; 68% Black). More than 40% of the study group had a BMI ≥ 30 kg/m2.

For each study participant, two sets of triplicate BP measurements were obtained using a regular-size adult automated BP monitor cuff and the cuff that fit their arm best after sizing. Prior to each set of readings, participants were asked to walk a similar distance from a waiting area to the room where BP was measured. Patients were seated and BP measurements were started 5 minutes after cuff placement, with no speaking during measurements. Each of the three sequential automated measurements were taken 30 seconds apart.  

In individuals whose arm measurements indicated they required a small adult cuff, the regular cuff resulted in a nearly 4 mm Hg-lower systolic pressure and a 1.5 mm Hg-lower diastolic pressure. For those whose arm measurements indicated a large cuff was required, systolic readings were nearly 5 mm Hg higher than with the appropriate cuff and diastolic readings were about 2 mm Hg higher (P < 0.001 for both comparisons). Finally, in those requiring an extra-large cuff, using a regular-size adult cuff overestimated systolic pressure by 19.7 mm Hg and diastolic pressure by 7.4 mm Hg compared with the appropriate cuff (P < 0.001 for both comparisons).

Among participants with a BP ≥ 130/80 mm Hg as measured by their correct cuff size, overestimation of BP due to undercuffing resulted in a misclassification in 39%, while underestimating BP due to overcuffing missed 22%.

“We know that there are a lot of low- and middle-income countries where there is often only one cuff that's available at the time of the healthcare encounter,” Brady said. “That was really our motivation to see how big of an impact the [cuff size] makes. We expected that there was going to be a difference, but we didn't expect to see this magnitude of difference.”

Even in North America, Brady said many clinics and offices likely don’t have multiple cuff sizes readily available without a staff member or physician having to hunt them down.

The issue takes on additional significance for patients who record at-home BP measurements. “This was a big struggle with the pandemic trying to conduct telemedicine with my patients, because I had to guide them in which cuff or which device to purchase so that they were appropriate for their arm,” Brady noted. “If you need an extra-large cuff, often the regular devices that are just sitting on the shelf in the pharmacy do not accommodate those arms, and you have to buy either a special device or you have to pay an additional $25 to $50 dollars to get the cuff that's appropriate.”

Lutsey stressed that arm size is a fluid dynamic that should be measured with frequency during BP checks, since patients can gain or lose weight from one healthcare encounter to the next for any variety of reasons.  

“I think this is very pragmatic in terms of thinking about how we can change the quality of care in the community [by] getting more accurate measurements so that blood pressure can be managed better,” she added.