We have been measuring blood pressure wrong, say Johns Hopkins doctors

A study led by researchers at Johns Hopkins Medicine reveals that the way a patient’s arm is positioned during routine blood pressure (BP) screenings can lead to significant overestimation of results, potentially contributing to the misdiagnosis of hypertension.

The study highlights that commonly used arm positions, such as resting the arm on the lap or leaving it unsupported at the side, can inflate BP readings by up to 7 mmHg in systolic pressure (the upper number in a BP reading).

The findings are significant given that nearly half of U.S. adults have elevated blood pressure, according to the American Heart Association (AHA). Because the condition often presents without noticeable symptoms, early and accurate detection is crucial, especially during routine checkups.

The worst positions to measure BP in

Lead author Dr. Tammy Brady, vice chair for clinical research in the Department of Pediatrics at the Johns Hopkins University School of Medicine, said the study confirms that arm position during BP measurement makes a “huge difference” in the accuracy of the results. Dr. Brady emphasized that even small deviations from recommended guidelines can have a substantial impact on patient diagnosis and treatment.

The study tested the effects of three arm positions on blood pressure measurements: resting the arm on a desk, resting it on a lap, and leaving the arm unsupported at the patient’s side.

According to the findings, the lap support position overestimated systolic BP by an average of 3.9 mmHg and diastolic BP (the lower number in a BP reading, which measures the pressure between heartbeats) by 4.0 mmHg. The unsupported arm at the side position was even more inaccurate, overestimating systolic BP by 6.5 mmHg and diastolic BP by 4.4 mmHg.

To test their hypothesis, the researchers recruited 133 participants between the ages of 18 and 80, with a study group that was 78% Black and 52% female. The results underscored the impact of improper arm positioning during BP screening. The overestimation caused by incorrect arm positioning, particularly the unsupported arm at the side, could easily lead to misdiagnoses of hypertension.

For example, Sherry Liu, a co-author of the study, noted that an overestimated systolic BP by 6.5 mmHg could result in a reading of 130 or higher, which classifies as stage 2 hypertension .

Measuring BP correctly

The authors cautioned that while their findings apply to BP readings taken with automated devices, the results might not extend to other BP measuring devices. Nonetheless, the study’s conclusions are clear: clinicians must pay closer attention to proper BP measurement techniques, and patients should advocate for themselves to ensure their arm is correctly positioned during BP readings.

Dr. Brady stressed the importance of following clinical guidelines for accurate BP measurements, which include the use of the correct cuff size, ensuring back support for the patient, uncrossed legs with feet flat on the floor, and proper arm support.

Specifically, the guidelines recommend placing the arm at heart level, supported on a firm surface such as a desk or table. Despite these clear recommendations, Dr. Brady noted that BP screenings are often performed with patients seated on exam tables without adequate arm support, leading to potential overestimations that could alter a patient’s diagnosis.

Dr. Brady emphasized that even small inaccuracies could lead to unnecessary treatments or medications, which could impact a patient’s quality of life. Given that high blood pressure is often managed through lifestyle changes and medication, proper diagnosis is crucial to avoid both over- and under-treatment.

The study has been published in JAMA Internal Medicine .