How Incorrect Arm Positions Might Affect Your Blood Pressure Readings

How do you hold your arm when getting your blood pressure measured? You could get different results if you rest your arm on a table, on your lap, or hang your arm at your side, according to a new study.

In a study published on October 7 in JAMA Internal Medicine, researchers measured people’s blood pressure in these three different arm positions. They found that when participants deviated from standard guidelines—resting the arm on a desk or other hard surface—they had higher blood pressure measurements.

Experts warn these artificially high blood pressure readings could raise the risk of an unnecessary hypertension diagnosis.

“We didn’t expect to see such a big difference, and one that could potentially lead to a change in diagnosis,” study author Tammy Brady, MD, PhD, associate professor and vice chair for clinical research in the department of pediatrics at the Johns Hopkins University School of Medicine, told Health.

The study “highlights the importance of proper blood pressure measurement technique in the office,” added Eugene Yang, MD, clinical professor and co-director of the Cardiovascular Wellness and Prevention Program at the University of Washington School of Medicine.

Here’s what experts had to say about why your blood pressure reading can change based on your arm position and how to ensure you’re getting the most accurate reading possible.

To further explore how “commonly used, nonstandard arm positions” affect blood pressure readings, Brady and her colleagues recruited 133 participants—the average age was 57, and 36% had high blood pressure.

The researchers measured the participants’ blood pressure three times. For one measurement, the participants had their arms supported on a desk with the cuff positioned around heart level, in line with standard guidelines. The second position involved the participants resting their arms on their laps, while the final measurement was taken while participants hung their arms at their side.

In their study, improper arm position led to inflated systolic and diastolic blood pressure, represented by the top and bottom numbers of the blood measurement device, respectively. The average blood pressure measurement was 126/74 mm Hg in the standard position, 130/78 mm Hg for the lap position, and 133/78 mm Hg for the side position.

That means resting your arm in your lap during the measurement increased both systolic and diastolic blood pressure by 4mm Hg. But resting your arm by your side had a greater impact, raising systolic blood pressure by 6.5 mm Hg and diastolic by 4.4 mm Hg.

These findings highlight how the blood pressure cuff should be kept near heart level for the most accurate results, Florian Rader, MD, medical director of the Hypertension Center at the Cedars-Sinai Smidt Heart Institute, told Health.

Blood pressure measures how much blood is pushing against the walls of your blood vessels. The top number, the systolic pressure, measures the force during the heartbeat. The lower number, diastolic pressure, measures the force in between beats.

The force of gravity being exerted on the arm in nonstandard positions, Brady explained, requires blood vessels to work harder to return blood to the heart.

“In a closed fluid system, pressure varies depending on the level at which it’s measured, similar to how the pressure you feel increases as you dive deeper into a pool,” Francis Alenghat, MD, PhD, associate professor of medicine and co-director of the cardiovascular diseases fellowship at the University of Chicago Medical Center, told Health.

“Since we’re most concerned with the pressure that the heart experiences, blood pressure measurements should be taken at the level of the heart, which is why placing the arm on a desk or table is recommended,” he explained.

Additionally, when a person holds their arm on their lap or hangs it in the air, the arm muscles in those positions are contracted, or aren’t at rest—this can further increase blood pressure, Brady said.

The study found relatively small variations between the three blood pressure readings, however, experts said these inaccuracies can lead to larger issues.

For example, if someone with a systolic blood pressure of 126 mm Hg holds their arm incorrectly, they could have a reading of 130 mm Hg, leading to an unnecessary hypertension diagnosis. They could be prescribed medications that they don’t need, raising the risk of unwanted side effects.

“This can have significant consequences when making decisions about whether someone needs to be treated for hypertension,” Yang said.

However, other experts said the differences might not be overly substantial or dangerous for a person’s health.

“The differences in blood pressure between measuring at the heart level and with the arm hanging down are small,” Alenghat said. “I suspect a measurement with the arm hanging down would be unlikely to result in a major over-treatment that would cause a patient’s blood pressure to drop dangerously low.”

In addition to resting your arm on a flat surface, it’s important to wear a proper-fitting arm cuff, plant your feet on the ground, and keep your legs uncrossed to ensure you’re getting an accurate blood pressure reading.

But getting an accurate blood pressure reading depends on both the patient and the provider. In a previous study, Brady found that the blood pressure measurements taken by doctors or nurses in a triage setting differed from measurements taken using best practices more than half the time.

“One thing that’s maybe under-appreciated is the need—not only for initial education and certification of the staff who are measuring blood pressures—but also the need for recertification every six months,” said Brady. “Skill decay happens over time, impacting measurement accuracy.”

Even when the standard guidelines are being followed, some people may still see artificially high readings when they go to the doctor—this is often attributed to “white coat hypertension” or the stress of being in a doctor’s office.

As a result, some people may want to take multiple measurements at home to confirm whether their blood pressure is actually elevated.

To ensure these at-home readings are accurate, the American Heart Association recommends:

“Clinicians must educate patients on how to measure their blood pressures correctly at home,” Yang said. “Mistakes made at home will cause inaccurate readings that could lead to over-treatment of blood pressure.”