Can the Position of Arm During Blood Pressure Screening Overestimate Test Results? Study Explores the Impact

A study led by Johns Hopkins Medicine researchers concludes that commonly used ways of positioning the patient's arm during blood pressure (BP) screenings can substantially overestimate test results and may lead to a misdiagnosis of hypertension.

In a report on the study, published in JAMA Internal Medicine, investigators examined the effects of three different arm positions: an arm supported on a desk, arm supported on a lap, and an unsupported arm hanging at the patient's side. Researchers found that lap support overestimated systolic pressure (the top number in a BP reading) by nearly 4 mmHg, and an unsupported arm hanging at the side overestimated systolic pressure by nearly 7 mmHg.

The findings confirm that arm position makes a "huge difference" when it comes to an accurate blood pressure measurement, says Tammy Brady, M.D., Ph.D., vice chair for clinical research in the Department of Pediatrics at the Johns Hopkins University School of Medicine, medical director of the pediatric hypertension program at Johns Hopkins Children's Center, deputy director of the Welch Center for Prevention, Epidemiology, and Clinical Research and senior author of the study. And they underscore the importance of adhering to clinical guidelines calling for firm support on a desk or other surface when measuring blood pressure, the investigators add.

The latest clinical practice guidelines from the American Heart Association emphasize several key steps for an accurate measurement -- including appropriate cuff size, back support, feet flat on the floor with legs uncrossed, and an appropriate arm position, in which the middle of an adjustable BP cuff is positioned at mid-heart level on an arm supported on a desk or table.

Despite these recommendations, the researchers say BP is too often measured with patients seated on an exam table without any, or inadequate, arm support. In some cases, a clinician holds the arm, or the patient holds an arm in their lap. In the new Johns Hopkins study, the researchers recruited 133 adult participants (78% Black, 52% female) between Aug. 9, 2022, and June 1, 2023. Study participants, who ranged from age 18 to 80, were sorted at random into one of six possible groups that differed by order of the three seated arm positions. Measurements were taken during a single visit between 9 a.m. and 6 p.m. Before BP measures were taken, all participants first emptied their bladders and then walked for two minutes to mimic a typical clinical scenario in which people walk into a clinic or office before screening takes place. They then underwent a five-minute, seated rest period with their backs and feet supported. Each person, wearing an upper arm BP cuff selected and sized based on their upper arm size, had three sets of triplicate measurements taken with a digital blood pressure device 30 seconds apart.

Upon completion of each set of three measurements, the cuff was removed, participants walked for two minutes and rested for five minutes. In the same visit, they then underwent a fourth set of triplicate measurements with their arm supported on a desk, a set used to account for well-known variations in BP readings.

Researchers found that BP measurements obtained with arm positions frequently used in clinical practice -- an arm on the lap or unsupported at the side -- were markedly higher than those obtained when the arm was supported on a desk, the standard, recommended arm position. Supporting the arm on the lap overestimated systolic BP -- the top number of a reading, or the force of blood flow when pumped out of the heart, by 3.9 mmHg and diastolic blood pressure -- the bottom number, or the pressure in the arteries when the heart rests between beats, by 4.0 mmHg. An unsupported arm at the side overestimated systolic by 6.5 mmHg and diastolic by 4.4 mmHg.