Wrong arm placement could be affecting blood pressure readings for millions: study

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The improper placement of a patient arms could be leading to massive overdiagnosis of high blood pressure (BP) across the United States, according to a new study.

“Hypertension is the leading cause of cardiovascular disease and preventable mortality worldwide,” said the original investigation, “Arm Position and Blood Pressure Readings: The ARMS Crossover Randomized Clinical Trial,” published this month in JAMA Internal Medicine. Measuring it correctly is a cornerstone of diagnosing and treating it, the researchers said.

To do so, patients should have the appropriate cuff size for the arm, back support, and their feet on the floor with uncrossed legs. Where does their arm go? Ideally, resting on a desk or table with the midcuff level with the heart.

“Despite these recommendations, proper arm position is commonly overlooked in daily practice,” with patients seated on examination tables and resting the arm in their lap, hanging it at their side, or having a health care professional hold it up, the study said.

‘BP is greatly overestimated’

The placement makes a difference, according to the researchers at the Johns Hopkins University School of Medicine. From August 2022 to June 2023, they recruited 133 patients who would walk for two minutes to replicate a typical clinical scenario before arriving at a BP measuring station. After five minutes’ seated rest, the researchers took three BP measurements from the right arm and compared the results based on location of the patients’ arms – on the desk, in their laps, or at their sides. They repeated the cycle until each patient had four sets, or 12 total readings.

The results: Higher blood pressure readings depending on arm placement. The average systolic blood pressure over diastolic blood pressure (SBP/DBP) was 126/72 mm Hg for desk positions, compared with 130/78 mm Hg for lap positions, and 133/78 mm Hg for the side positions.

“We demonstrate that when the arm is completely unsupported and hanging at the side, as is often the case when arm support on a desk or chair is not possible or when a patient is seated on the examination table in a clinic room, BP is greatly overestimated,” the study said. “Furthermore, positioning the arm in the lap, a typical compromise for the above scenarios, also results in considerable BP overestimation. Thus, these arm positions should not be used, even in the setting of limited time or resources.”

Why the difference?

Clinicians may overlook ideal arm placement due to lack of awareness and limitations in training, resources and equipment, the study said. The authors also suggested several physiological reasons for the differences. Those include gravitational pull on blood and subsequent increase in vasoconstriction within the body, and potential muscular constriction.

As the numbers of patients add up, the error in BP measurement could “lead to substantial hypertension overdiagnosis, unnecessary patient follow-ups, and overtreatment,” the study said.

How much overdiagnosis? As many as 40 million patients misclassified as hypertensive using an SBP cutoff of 140 mm Hg and higher, or 54 million patients misclassified when using the SBP cutoff of 130 mm Hg or higher, according to the study.

As a remedy, the researchers suggested health systems should make efforts – possibly even regulations – to ensure accurate BP measurements. The problem could affect patients taking BP readings at home. “Therefore, education and training of both clinical staff and patients regarding BP measurement is essential for hypertension control and cardiovascular disease prevention,” the study said.

While the measurement of patient blood pressure is ubiquitous in health care, the researchers noted few studies have rigorously evaluated the effects of arm position, and previous analyses were limited by suboptimal design.