Arm Position Matters for Accurate Blood Pressure Readings

Small changes in positioning can lead to big changes in your blood pressure readings, which can impact your heart health and treatment plan. 

A new study led by researchers at Johns Hopkins Medicine has found that how your arm is positioned when taking blood pressure readings can significantly affect the results. Published in JAMA Internal Medicine, the study reveals that common nonstandard arm positions often used in clinical settings can lead to an overestimation of blood pressure (BP), potentially leading to misdiagnosis of hypertension.

The study tested three different arm positions on 133 adults:

 - Arm supported on a desk (the standard recommended position): This is the position recommended by clinical guidelines, where the arm is placed at heart level and supported on a firm surface.

 - Arm resting on the lap: This position overestimated systolic BP (the top number) by 3.9 mmHg and diastolic BP (the bottom number) by 4.0 mmHg.

 - Arm unsupported at the side: This resulted in even greater overestimation, with systolic BP increasing by 6.5 mmHg and diastolic BP by 4.4 mmHg.

These differences are significant, as an overestimation of even a few millimeters of mercury (mmHg) could result in a patient being wrongly diagnosed with hypertension, leading to unnecessary treatments.


Blood pressure measurement is a delicate process, and the position of your arm can change the pressure in your arteries. When the arm is not at heart level or unsupported, gravity or muscle tension may increase the blood pressure reading.

To get the most accurate blood pressure reading, the American Heart Association recommends:

 - Sitting with your back supported.

 - Keeping your feet flat on the floor.

 - Using an appropriately sized blood pressure cuff.

 - Supporting your arm on a firm surface, such as a desk or table, with the middle of the cuff at heart level.

While supporting your arm on a desk is ideal, other acceptable positions include:

 - Arm supported by the arm of a chair, as long as the arm remains at heart level.

 - Arm supported by a pillow or cushion, again keeping it at heart level.

In addition to the arm’s position, the position of the BP instrument is also important. Ideally, the device—whether a mercury sphygmomanometer or a digital monitor—should be at the same level as your heart. If the instrument is positioned too high or too low, it can also alter the reading, leading to inaccurate blood pressure results. Surprisingly, this crucial factor is often overlooked in many clinical guidelines.


REFERENCE

Hairong Liu et al, Arm Position and Blood Pressure Readings, JAMA Internal Medicine (2024). Published online October 7, 2024. doi:10.1001/jamainternmed.2024.5213

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