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For Accurate BP Measurement, Cuff Size Must Be "Just Right"
Blood pressure cuffs that are too large or too small for an individual's upper arm return measurements that may misguide therapeutic decisions, say study authors.
In a cohort of community dwelling adults using an automated blood pressure (BP) device, use of a “regular” size arm cuff vs a cuff appropriate for an individual’s arm size resulted in “strikingly inaccurate” BP readings, according to authors of the Cuff(AZ) trial, published August 7 in JAMA Internal Medicine.1
Clinically and statistically significant lower (cuff too large) and higher (cuff too small) measurements were consistent across appropriate cuff sizes but were most pronounced in individuals with larger arms, according to Tammy M Brady, MD, PhD, associate professor of pediatrics at Johns Hopkins University School of Medicine in Baltimore, and coauthors.
Specifically, for study participants who needed a large or extra-large cuff size, the use of a regular size cuff resulted in 4.8-mm Hg and 19.5-mm Hg higher systolic BP (SBP) readings, respectively, than with an appropriate size cuff (both P<.001). On the other hand, for participants who should have been using a small cuff, the result of using a regular size cuff was a SBP reading 3.6 mm lower (P<.001).1
Readings for diastolic BP (DBP) also were consistently inaccurate for participants who used cuffs that were 1 size too large (-1.3 mm Hg); 1 size too small (1.8 mm Hg); and 2 sizes too small (7.4 mm Hg) (P<.001 for both small sizes).
The findings are particularly concerning, the authors wrote, given the many settings where a single standard size adult cuff is used routinely for all individuals, regardless of arm size.1
Writing in an accompanying editorial,2 LaPrincess C Brewer, MD, MPH, of the Mayo Clinic College of Medicine in Rochester, Minnesota, and co-authors said, "These findings are especially relevant for under-resourced clinics, such as federally qualified health centers, that are often not adequately equipped and instructed to measure BP correctly." These clinics, they added, “predominantly serve marginalized populations, such as racial and ethnic minority groups and socioeconomically disenfranchised individuals, who face CVD [cardiovascular disease] disparities.” Providing them with resources to correctly measure BP "is a key strategy to achieving health equity."2
Brady and colleagues note that while discrepancies related to wrong cuff size have been reported in studies of BP methods that use manual auscultation, there is no “rigorous study” of the issue with automated oscillometric BP devices, which use a fundamentally different technique to estimate BP.1
Automated BP measurements for hypertension are endorsed by the 2017 adult hypertension guidelines3 and are widely used in clinical settings and for home blood pressure monitoring as well, wrote Brady et al. The study authors cited research that found a regular size BP cuff is appropriate for only half of US adults while 40% would require a large cuff. Most home-use BP monitors come with a regular size cuff, they cautioned, suggesting that the 40% or more of US adults who might require a large arm cuff size for home BP measurement would obtain home BP readings overestimated by almost 5 mm Hg.1
The Cuff(SZ) study was designed to determine the effects of “overcuffing” and “undercuffing” vs appropriate cuffing and to describe the effects of cuffing errors on BP reading across multiple cuff sizes.
The Cuff(SZ) randomized, cross-over trial
Brady and team recruited 195 participants with screening events at a public food market and a senior housing facility, and through mailings to prior study participants and study brochures in hypertension clinics at Johns Hopkins University. Mean participant age was 54 years; 34% were men and 68% self-identified as Black. Approximately half (51%) had hypertension, 20% had diabetes, and mean BMI was 28.8. Small, regular, large, and extra-large cuffs were appropriate for 35, 54, 66, and 40 participants, respectively.1
Participants had their BP measured 3 times with each of the 4 cuff sizes in random order with 30 seconds between each of the 3 readings. The fourth measurement was taken with an appropriately sized cuff. All participants had their BP taken with the "regular" sized cuff at least once. Measurements were taken between 9 am and 6 pm and all participants followed the same protocol: Bladders were empty; they took a 2-minute walk before each set of measurements followed by 5 minutes of rest.
Secondary outcome. In addition to the primary outcomes noted above, the secondary outcome—difference in BP obtained with too-small or too-large BP cuffs compared with an appropriate size—found that among those requiring a small BP cuff or an extra-large BP cuff, the magnitude of BP difference was greater when the BP cuff was 2 sizes different compared with 1 size different and the magnitude of these BP differences increased incrementally as the appropriate cuff size progressed from the regular BP cuff to the extra-large BP cuff.1
Among study limitations the authors noted insufficient subgroup sample size in some groups (like too few participants with hypertension and obesity in the small-cuff group); heterogeneity of magnitude and direction of BP misreadings between individuals; the rigorous training researchers had, which might not be seen in a clinical setting; and a lack of applicability for individuals with "extreme arm circumferences," for example <20 cm or >55 cm.1
