For accurate blood pressure measurement, cuff size matters

A thought-provoking editorial in the August issue of American Family Physician discussed the reasons for the divergence in treatment guidelines for mild hypertension that followed the publication of the Systolic Blood Pressure Intervention Trial (SPRINT). Dr. Stephen Martin noted that “in SPRINT, blood pressure was measured using ideal techniques that are unlikely to be replicated using standard practice.” These blood pressure (BP) measurement practices, described in a 2018 editorial about the American College of Cardiology/American Heart Association (ACC/AHA) hypertension guideline and reiterated in a clinical review article on home BP monitoring, include using an appropriately sized blood pressure cuff:

To determine cuff size, patients should measure their arm circumference at the midpoint of the upper arm. The bladder length should be 75% to 100% of the arm circumference, and bladder width should be 37% to 50% of the arm circumference.

Four adult BP cuff sizes are available in the United States: small (20 to 25 cm mid-arm circumference), regular (25.1 to 32 cm), large (32.1 to 40 cm), and extra-large (40.1 to 55 cm). Although most primary care offices have cuffs in multiple sizes, home BP monitors sold in pharmacies typically use the regular cuff size, which is too small for many adults.

Just how inaccurate is an automated BP reading in an adult patient wearing a cuff that is too small or too large? To answer this question, researchers from Johns Hopkins University performed a randomized crossover trial in 195 community-dwelling adults. The mean age was 54 years, and about one-half had a BP higher than 130/80 mm Hg when using an appropriately sized cuff. Researchers determined that a regular size cuff was appropriate for 54 study participants, whereas 35 required a small cuff and 106 required a large or extra-large size.

Each participant had four sets of triplicate BP measurements, using a cuff size that was appropriate, too small, or too arge in random order, followed by an appropriately sized cuff. Participants for whom a large or extra-large cuff size was appropriate had their systolic BPs overestimated by about 5 and 20 mm Hg, respectively, when using a regular size cuff. Diastolic BP overestimations were smaller but still statistically significant (1.8 and 7.4 mm Hg). Conversely, participants for whom a small cuff size was appropriate had their systolic BP underestimated by 3.6 mm Hg when wearing a regular size cuff. A recent analysis found that more than half of U.S. adults need a large or extra-large size, and the study authors noted the immense global implications of using cuffs that are too small:

In this context, 40% or more U.S. consumers would obtain BP readings overestimated by almost 5 mm Hg when conducting home BP monitoring. On a global scale, an error in SBP measurement of 5 mm Hg could lead to the misclassification of 84 million people to either undertreatment or overtreatment of hypertension.

In a table summarizing lessons learned and cautions raised by SPRINT, Dr. Martin warned, “Prevention and associated overdiagnosis can divert our attention from sick patients to healthy patients.” Whether family physicians and their patients are aiming for the ACC/AHA guideline’s lower BP targets or the 140/90 mm Hg target recommended for most people by the American Academy of Family Physicians, using an appropriately sized cuff is critical to avoid overdiagnosing healthy adults with hypertension.

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