How do you hold your arm when you measure your blood pressure? You might get different results if you rest your arm on a table, in your lap, or hang your arm out to the side, according to a new study.

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

Experts warn that these artificial blood pressure values ​​could increase the risk of an unnecessary high blood pressure diagnostic.

“We did not expect to see such a large difference and one that could lead to a change in diagnosis,” study author Tammy Brady, MD, PhDassociate professor and vice chair for clinical research in the department of pediatrics at Johns Hopkins University School of Medicine, said Health.

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

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

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

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

In their study, incorrect arm position led to systolic swelling and diastolic blood pressure, represented by the top and bottom numbers of the blood measuring device, respectively. The mean 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.

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

These findings highlight how the blood pressure cuff should be kept close to the level of the heart for the most accurate results, Dr. Florian Radersaid Cedars-Sinai Heart Institute Medical Director Smidt Hypertension Center Health.

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

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

“In a closed fluid system, the pressure varies depending on the level at which it is measured, similar to how the pressure you feel increases as you sink deeper into a pool.” Francis Alenghat, MD, PhDassociate professor of medicine and co-director of the Cardiovascular Disease Fellowship at the University of Chicago Medical Center, said Health.

“Because we are most concerned with the pressure 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.

In addition, when a person holds their arm in their lap or hangs it in the air, the arm muscles in those positions are contracted or not at rest — which 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 bigger problems.

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 diagnosis of high blood pressure. They could be prescribed drugs they don’t need, increasing the risk of unwanted side effects.

“This can have significant consequences when making decisions about the need for treatment for high blood pressure,” Yang said.

However, other experts said the differences may not be too substantial or dangerous to a person’s health.

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

In addition to resting your arm on a flat surface, it is important to wear a suitable arm cuffplant your feet on the ground and keep your legs uncrossed to ensure you get 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 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 probably under-appreciated is the need — not only for initial education and certification of blood pressure personnel — but also the need for recertification every six months,” Brady said. “Skill degradation occurs over time, affecting measurement accuracy.”

Even when standard guidelines are followed, some people may still see artificially high values ​​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 more measurements at home to confirm whether their blood pressure is actually high.

To ensure them readings at home are correct, the American Heart Association recommends:

• Avoid smoking, caffeine, or exercise 30 minutes before taking your blood pressure
• Going forward to the bathroom
• Removing clothes from the arm
• Sit still for at least five minutes without talking or using your phone
• Sitting with your back straight in a chair, legs uncrossed and flat on the floor
• Resting the arm on a flat surface and placing the cuff at heart level
• By measuring at the same time each day and taking two readings
• Talk to a healthcare professional about how often to take your blood pressure

“Clinics need to educate patients on how to properly measure their blood pressure at home,” Yang said. “Mistakes made at home will cause inaccurate readings that could lead to overtreatment of blood pressure.”