By Science Daily (Science) | Created at 2026-10-01 14:14:15 | Updated at 2026-10-01 22:19:54
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A Johns Hopkins Medicine-led study suggests that the way a patient positions their arm during a blood pressure (BP) check can meaningfully affect the result. Common arm positions used during screenings may make blood pressure appear higher than it actually is, potentially contributing to an incorrect diagnosis of hypertension.
In a report on the study, published in JAMA Internal Medicine, researchers compared three arm positions: an arm supported on a desk, an arm supported on a lap, and an unsupported arm hanging at the patient's side. They found that resting the arm on the lap increased systolic pressure (the top number in a BP reading) by nearly 4 mmHg, while allowing the arm to hang unsupported at the side increased systolic pressure by nearly 7 mmHg.
Arm position can make a major difference
The results show that arm position makes a "huge difference" in obtaining an accurate blood pressure measurement, according to 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.
The researchers say the findings reinforce clinical recommendations that call for the patient's arm to be firmly supported on a desk or another surface during blood pressure measurement.
According to the American Heart Association, nearly half of U.S. adults have elevated blood pressure, a diagnosis made when the measured force of blood flowing through blood vessels is higher than what is generally considered normal, on average 120/80. If left untreated, high blood pressure can increase the risk of heart attack, stroke and other serious cardiovascular problems.
Hypertension often produces few or no noticeable symptoms, making early and regular screening during routine medical visits an important part of managing the condition. In many cases, blood pressure can be controlled through lifestyle changes such as weight loss, healthy diets and exercise, along with treatment using any of a variety of medications.
How blood pressure should be measured
The latest clinical practice guidelines from the American Heart Association outline several steps intended to improve measurement accuracy. These include using an appropriate cuff size, supporting the back, keeping the feet flat on the floor with the legs uncrossed, and positioning the arm correctly. The middle of an adjustable BP cuff should be at mid-heart level while the arm rests on a desk or table.
Despite those recommendations, the researchers say blood pressure is frequently checked while patients sit on an exam table with little or no support for their arms. Sometimes a clinician holds the patient's arm, while in other cases the patient rests the arm in their lap.
For the Johns Hopkins study, researchers enrolled 133 adult participants (78% Black, 52% female) between Aug. 9, 2022, and June 1, 2023. Participants ranged in age from 18 to 80 and were randomly assigned to one of six groups that differed in the order in which the three seated arm positions were tested.
All measurements were collected during a single visit between 9 a.m. and 6 p.m. Before blood pressure was measured, participants emptied their bladders and walked for two minutes to simulate the typical experience of walking into a clinic or medical office before a screening. They then rested while seated for five minutes, with their backs and feet supported.
Each participant wore an upper arm BP cuff chosen according to the size of their upper arm. Researchers used a digital blood pressure device to collect three sets of three measurements, with 30 seconds between individual readings.
Researchers carefully controlled each measurement
After each group of three readings, researchers removed the cuff. Participants then walked for two minutes and rested for another five minutes. During the same visit, each person completed a fourth set of three measurements while their arm was supported on a desk. This additional set was included to account for the well known variation that can occur between blood pressure readings.
Every measurement took place in a quiet, private setting. Participants were also instructed not to speak with researchers or use their phones while their blood pressure was being checked.
The results showed that two arm positions commonly seen in clinical practice, resting the arm on the lap or leaving it unsupported at the side, produced substantially higher blood pressure measurements than the recommended position of supporting the arm on a desk.
Resting 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. It also overestimated diastolic blood pressure, the bottom number, or the pressure in the arteries when the heart rests between beats, by 4.0 mmHg.
Leaving the arm unsupported at the side produced an even larger difference. Systolic pressure was overestimated by 6.5 mmHg, while diastolic pressure was overestimated by 4.4 mmHg.
A difference large enough to affect diagnosis
"If you are consistently measuring blood pressure with an unsupported arm, and that gives you an overestimated BP of 6.5 mmHg, that's a potential difference between a systolic BP of 123 and 130, or 133 and 140 -- which is considered stage 2 hypertension," says Sherry Liu, M.H.S., an epidemiology research coordinator at the Welch Center for Prevention, Epidemiology, and Clinical Research, Department of Epidemiology, at Johns Hopkins Bloomberg School of Public Health and study author.
The investigators note that the findings may apply only to blood pressure measurements taken with automated devices. The results may not necessarily extend to readings collected with other types of blood pressure equipment.
Brady says the findings nevertheless show why clinicians should follow recommended measurement procedures more carefully. She also says patients "must advocate for themselves in the clinical setting and when measuring their BP at home."
Along with Brady and Liu, authors from Johns Hopkins are Di Zhao, Ahmed Sabit, Chathurangi Pathiravasan, Junichi Ishigami, Jeanne Charleston, Edgar Miller III, Kunihiro Matsushita and Lawrence Appel.
This study was supported by Resolve to Save Lives, which is funded by Bloomberg Philanthropies, the Bill and Melinda Gates Foundation and Gates Philanthropy Partners, which is funded with support from the Chan Zuckerberg Foundation.
