Certain arm positions commonly used for blood pressure checks can lead to inaccurate results. Here’s the right way to do it

A new study has found that having your arm in the wrong position during blood pressure checks – at home or at the doctor’s – can result in readings that are “significantly higher” than when your arm is in the recommended position: The Right Way supported on a table with the center of the cuff level with the heart.

This suggests that failing to consistently properly position and support your arm while measuring blood pressure could result in a misdiagnosis of high blood pressure, which some experts fear could potentially lead to unnecessary treatment.

The study, published Monday in the journal JAMA Internal Medicine, found that resting your arm in your lap during a blood pressure reading can lead to an overestimated systolic blood pressure reading by 3.9 mm Hg and an overestimated diastolic blood pressure reading by 4 mm Hg. And letting your arm hang at your side can lead to an overestimated systolic reading by 6.5 mm Hg and an overestimated diastolic reading by 4.4 mm Hg.

Blood pressure is measured in units of millimeters of mercury or mm Hg, which consists of two numbers: the upper or systolic value and the lower or diastolic value. A person is considered to have high blood pressure or hypertension if they have consistent readings of 130/80 or higher.

“Healthcare providers need to be reminded of the importance of taking the time to perform these steps correctly,” said the study’s senior author, Dr. Tammy Brady, who is vice chair for clinical research in the department of pediatrics at Johns Hopkins University. School of Medicine and medical director of the Pediatric Hypertension Program at Johns Hopkins Children’s Center.

“I just hope it raises awareness of how important things like arm position are to the accuracy of blood pressure readings,” Brady said of the study.

“I also hope that this study educates patients, empowering them to advocate for proper measurements in a clinic,” she said. “But also because so many patients rely on home blood pressure measurements for the diagnosis, evaluation and treatment of hypertension, I hope this teaches them how to position their arms correctly, because our findings definitely extend to home measurements.”

The Johns Hopkins University researchers recruited 133 adults from Baltimore, Maryland, between August 2022 and June 2023 to participate in the study. The adults, ages 18 to 80, were randomly assigned to have their blood pressure measured while their arms were positioned in three different ways: supported on a desk, as is recommended standard practice; supported on their lap; or hanging by their side, unsupported.

Each study participant underwent a total of twelve blood pressure measurements with the arms in each of these different positions.

Among the participants, when their arms were supported on a desk, as recommended by standard clinical guidelines, the average of their blood pressure reading was 126/74, the researchers found.

But when the participants’ arms rested on their laps during their measurements, the average blood pressure reading was 130/78, and when their arms hung at their sides, the average of their measurements was 133/78.

“I didn’t expect there to be that much of a difference when the arms were placed in the two alternative positions. We tested those positions because these are the positions where most people’s blood pressure is measured, according to data and personal observations,” said Brady. “We thought there would be a difference, but I was surprised by how much difference there was.”

The researchers wrote that there are several physiological reasons why blood pressure readings may be falsely higher if the arm is not adequately positioned or supported. An increased vertical distance between the heart and the cuff placement site may increase the hydrostatic pressure in the arteries, or the pressure of the blood against the wall, due to gravity, leading to an overestimation of blood pressure. And an unsupported arm can cause the muscle to contract, which can cause an increase in blood pressure.

How to accurately monitor blood pressure

The new study results are consistent with a previous study that showed that unsupported arm positions or an arm placed below heart level can overestimate a blood pressure reading.

“We know that arm position affects blood pressure readings, what this study does is give us a more precise measure of how much this has an impact,” Dr. Nichola Davis, vice president and chief population health officer at NYC Health and Hospitals, who was not involved in the study, said in an email.

“This is seen in participants with all blood pressure levels, but more pronounced in participants with elevated blood pressure. These are important findings because we diagnose and treat hypertension based on blood pressure measurements, and these measurements must be accurate,” Davis said in the email.

The researchers wrote in the study that the “latest clinical practice guidelines emphasize several important steps for accurate measurements,” including:

• Wear the correct cuff size.

• Let your back be supported.

• Keep feet flat on the floor and legs uncrossed.

• Ensure correct arm position – the cuff should be placed at heart level with the arm supported on a desk or table.

Wearing the correct cuff size is critical because an incorrectly sized blood pressure cuff can distort blood pressure readings from automated blood pressure devices. A study published last year in the journal JAMA Internal Medicine found that using standard, full-size blood pressure cuffs resulted in “strikingly inaccurate” readings when a patient required blood pressure cuffs of different sizes, especially for participants wearing larger cuffs.

There are some steps people should take before getting their blood pressure checked, said Dr. Gail Adler, a cardiovascular endocrinologist and co-specialist at the hypertension clinic at Brigham and Women’s Hospital, who was not involved in the new study.

“In the 30 minutes before you measure your blood pressure, you want no smoking, no exercise, no caffeine, no alcohol and… no big fights. Don’t be psychologically stressed,” Adler said.

“What you want to do then is sit in the chair, get into the right position, and relax for five minutes, don’t talk, rest your arm comfortably, sit up straight with your back straight, don’t cross your legs and feet flat on the ground. Make sure you don’t have to urinate, if you do have to urinate or urinate, your blood pressure will increase,” she said. ‘And you’re not supposed to talk when you measure your blood pressure, and the cuff should be against your arm. So you don’t want to wear it over clothing.”

Because people often feel calmer and more comfortable at home, “we now find that studies suggest that blood pressure measured at home is a better indicator of your usual blood pressure than blood pressure measured in the office,” Adler said.

Blood pressure measurements are often “performed suboptimally” in clinical practice, which can lead to errors that then inappropriately alter physicians’ decisions about managing a patient’s blood pressure in about 20% to 45% of cases, according to the American Medical Association.

“Anecdotally, I think all of us on the research team have started to pay more attention to the way our blood pressure is measured. I have certainly paid attention to the way my children’s blood pressure is measured,” Brady said.

‘We should not make hasty judgments’

Having high blood pressure increases your risk of heart disease and stroke, the leading causes of death in the United States.

According to the U.S. Centers for Disease Control and Prevention, nearly half of adults in the United States are estimated to have high blood pressure, but only about 1 in 4 adults with high blood pressure have their blood pressure under control.

“I don’t think we are aggressive enough in America with treating hypertension,” said Dr. Dave Montgomery, a cardiologist at Piedmont Healthcare in Atlanta who was not involved in the new study, said in an email.

“Hypertension is one of the most common risk factors for cardiovascular disease and one of the easiest to treat and control. Yet hypertension is the culprit or leading cause of much of cardiovascular morbidity and mortality,” he said. “We miss the point too often.”

Regarding the new study, he added that he does not see a blood pressure reading that is off by 4 to 5 mm Hg – due to the position of the arms – that leads to overdiagnosis or overtreatment, in the form of a new prescription or dose adjustment.

“If someone has normal blood pressure, 4 mmHg will not change that. But in someone diagnosed with hypertension, 5 to 10 points can indicate that we don’t have quite the control we’re looking for,” Montgomery said. He added that blood pressure can change from minute to minute due to physical factors and a person’s psycho-emotional state.

“This means that we should generally not make hasty statements about one blood pressure measurement. But consistently high blood pressure should be treated aggressively,” he said. “This is how we reduce the burden of heart disease.”

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