Wrong positioning for BP screening could overestimate measurements

Key takeaways:

• Having the arm unsupported at the side or supported on the lap overestimated systolic and diastolic BP.
• Clinicians should be aware of and adhere to positioning guidelines, according to a researcher.

Commonly used ways of positioning a patient’s arm during BP screenings may significantly overestimate BP and result in misdiagnosis of hypertension and overtreatment, an analysis suggested.

According to Tammy M. Brady, MD, PhD and associate professor of pediatrics in the division of pediatric nephrology and medical director of the Pediatric Hypertension Program at Johns Hopkins University School of Medicine, and colleagues, proper arm position for BP screening “is commonly overlooked in daily practice,” while few studies have examined the impact of arm positioning on BP.

Healio previously reported on a study Brady and colleagues did last year, which showed that inaccurate BP cuff size was tied with incorrect BP measurements and diagnoses.

According to guidelines from the American Heart Association, patients should be seated in a chair with feet flat on the floor, their back supported and the arm wearing the BP cuff supported at heart level.

In the current crossover randomized clinical trial, published in JAMA Internal Medicine, 133 participants aged 18 to 80 years were assigned to sets of triplicate BP measurements with their arm positioned in three ways:

• supported on a desk;
• supported on the lap; and
• unsupported at the side.

The researchers noted that all participants underwent a fourth set of BP measurements with the arm supported on a desk to account for intrinsic BP variability, for a total of 12 BP measurements.

The primary outcomes were the difference in differences in mean systolic BP and diastolic BP between the desk position and the lap and side positions.

Among participants, 36% had a systolic BP of 130 mm Hg or higher, whereas 41% had a BMI of 30 or greater.

Brady and colleagues found that supporting the arm on the lap overestimated systolic BP by 3.9 mm Hg (95% CI, 2.5-5.2) and diastolic BP by 4 mm Hg (95% CI, 3.1-4.9).

Meanwhile, an arm unsupported at the side overestimated systolic BP by 6.5 mm Hg (95% CI, 5.1-7.9) and diastolic BP by 4.4 mm Hg (95% CI, 3.4-5.4).

These results were consistent across subgroups and greater among those at higher risk. For example, “[systolic] BP was overestimated by approximately 9 mm Hg among individuals with hypertensive BP when their arm was positioned at the side,” the researchers pointed out.

Sherry Liu, MHS, an epidemiology research coordinator at the Welch Center for Prevention, Epidemiology, and Clinical Research, explained in a press release that an overestimated systolic BP of 6.5 mm HG is “a potential difference between a systolic BP of 123 and 130, or 133 and 140 — which is considered stage 2 hypertension.”

The researchers explained that proper positioning could be overlooked in clinical practice for several reasons, such as a lack of awareness about the effect of positioning on BP measurements among health care providers.

There were several study limitations. The results may not be generalizable to other BP devices, while some subgroups had small sample sizes.

Brady said in the release that physicians need to do a better job of adhering to clinical guidance on positioning, while patients “must advocate for themselves in the clinical setting and when measuring their BP at home.”

References:

• Johns Hopkins Medicine study finds commonly used arm positions can substantially overestimate blood pressure readings. Available at: https://www.eurekalert.org/news-releases/1060145. Published Oct. 7, 2024. Accessed Oct. 7, 2024.
• Liu S, et al. JAMA Intern Med. 2024;doi:10.1001/jamainternmed.2024.5213.
• Where and how you sit matters when getting blood pressure taken at the doctor's office. Available at: https://www.heart.org/en/news/2023/11/09/where-and-how-you-sit-matters-when-getting-blood-pressure-taken-at-the-doctors-office. Published Nov. 9, 2023. Accessed Oct. 4, 2024.