Clarissa Chan, PharmD
A randomized crossover trial published in the October 2023 issue of JAMA Internal Medicine demonstrated that inappropriately sized BP cuffs significantly affected BP measurement accuracy.
Study overview and results
Researchers from Johns Hopkins University conducted the trial, which involved 195 community-dwelling adults in Baltimore, between March and October 2021.
The participants had varying mid-arm circumferences and a mean age of 54 years. Of these, 34% were male, 68% were Black, and 51% had hypertension. Study participants underwent four sets of triplicate BP measurements. The first three sets used an appropriate, too-small, or too-large cuff taken randomly, and the fourth set used an appropriately sized cuff.
Among individuals needing a small cuff, using a regular cuff resulted in a statistically significant lower BP reading (mean systolic BP difference of 3.6 mm Hg). In contrast, for those individuals requiring a large or extra-large cuff, using a regular cuff resulted in significantly higher BP readings (a mean systolic BP difference of 4.8 mm Hg and 19.5 mm Hg, respectively).
For participants requiring larger cuffs, BP differences were more pronounced with other cuff sizes. Findings were consistent across different systolic BP levels (≥130 mm Hg vs. <130 mm Hg) and BMI categories (≥30 kg/m² vs. <30 kg/m²).
To guarantee precision, the study researchers followed clinical practice guidelines, using a validated BP device under specific conditions. These conditions included ensuring an empty bladder; abstaining from caffeine, tobacco, and exercise for 30 minutes before readings; providing support for the arm, back, and feet; maintaining a quiet room environment; using an appropriate cuff size; and averaging triplicate readings, according to Tammy Brady, MD, PhD, who was part of the study and is co-chair on the AMA Validated Device List (VDL) independent review committee.
Validating for accuracy
BP readings are difficult to study and report accurately,” said Andy Lee, MD, from the University of California, Irvine School of Medicine. The benchmark, he said, is 24-hour ambulatory BP monitoring, which may be different from a single BP measurement done in a clinic.
Health care offices have medical-grade equipment that is independently verified and confirmed to be accurate. “The gold standard for comparison is a mercury sphygmomanometer, which is rare,” said Lee.
Additionally, Brady said patients should note that sizes are not standardized when buying a home BP device. Patients should ensure that one of the included cuffs is appropriately sized.
“Cuffs may not compress the brachial artery properly, leading to imprecise artery oscillation detection,” said Brady, an associate professor at Johns Hopkins University.
Individuals can check the U.S. National VDL at Validatebp.org to determine if cuffs are calibrated and validated for accuracy.
“Searching the cuff manufacturer’s site for AAMI/ISO validation testing is also an option,” said Brady. “Less than 20% of the devices on the market have ever been tested for accuracy.”
FDA never “approves” BP devices; they “clear” devices, which does not mean that a cuff has been tested for accuracy. Sites advertising FDA approval are making a false claim, noted Brady.
Patients are encouraged to bring their home equipment to health care offices in order to verify that their home measurements correspond with verified devices, said Lee.
Advice for patients to accurately measure BP
“Resting for 3 to 5 minutes prior to [BP] measurement is important for people with high BP to get the most accurate reading,” said Brady.
Arm position and loud or busy environments can also affect BP readings, said Brady.
She recommends patients measure their mid-arm circumference with a tape measure to choose the right cuff. “All cuffs have markings to inform [individuals] what arm circumference size [are appropriate],” she said.
“If a cuff pops off while inflating, it is too small. And if a cuff covers the elbow, it may be too big,” said Brady.
These implications are concerning for settings where a single regular BP cuff size is routinely used for all individuals. The researchers suggest a renewed emphasis on individualized BP cuff selection in clinical practice. ■
Pharmacists are also being encouraged to refer to CDC’s Using Pharmacists’ Patient Care Process to Manage High Blood Pressure, which incorporates a team-based care approach to prevent and manage high BP through five steps: Collect, Assess, Plan, Implement, and Follow-up: monitor and evaluate. The resource guide was co-developed by APhA and the American Medical Association along with CDC’s Division for Heart Disease and Stroke Prevention. Visit www.cdc.gov/dhdsp/pubs/docs/pharmacist-resource-guide.pdf to review the guide. ■