Keeping your blood pressure in range helps ensure cardiovascular health. However, new research shows that certain arm positions during blood pressure checks may cause inaccurate readings -- leading to possible misdiagnosis and improper care.

A study published in JAMA Internal Medicine, from Johns Hopkins University, recruited 133 adults, ages 18 to 80, between August 2022 and June 2023. The participants were randomly assigned to have their blood pressure measured while their arms were in three different positions: supported on a desk, as is the recommended standard practice; supported on their lap; or hanging by their side, unsupported. Each participant underwent a total of 12 blood pressure measurements with their arms in each of the three positions.

Researchers found that when the participants' arms were supported on a desk (as recommended by the standard clinical guidelines), the average of their blood pressure reading was 126/74. By comparison, when the participants' arms were resting in their laps during their readings, the average blood pressure reading was 130/78, and when their arms were hanging by their sides, the average reading was 133/78.

In other words, the results showed that having your arm resting in the lap during a blood pressure reading may lead to an overestimated systolic blood pressure measurement by 3.9 mm Hg and an overestimated diastolic reading by 4 mm Hg. And, having your arm hang by your side may lead to an overestimated systolic reading of 6.5 mm Hg and an overestimated diastolic reading of 4.4 mm Hg.

Normal blood pressure is typically below 140/90 mmHg, says Ian Del Conde Pozzi, M.D., cardiologist at Miami Cardiac & Vascular Institute, part of Baptist Health. "However, the optimal blood pressure -- associated with the lowest risk of cardiovascular complications -- is less than 120/80 mmHg." Maintaining blood pressure within this optimal range may significantly reduce the risk of heart disease, stroke, and other related conditions, he explains.

Arm position affects blood pressure accuracy because it influences the reading's relationship to heart level, says Danielle Belardo, M.D., preventive cardiologist in Los Angeles. "When the arm is lower than heart level, readings are artificially higher; if [the arm is] too high, readings may be falsely low," she says. Unsupported arm positions increase muscle tension, raising both systolic and diastolic pressure, she explains. Proper arm positioning avoids overestimations that can lead to misdiagnosis or over-treatment, allowing for accurate assessments and better patient care, she notes.

For the most accurate reading, the arm should be supported on a desk or surface, with the middle of the cuff aligned with the level of the heart, adds Dr. Del Conde Pozzi.

Several factors can contribute to inaccurate blood pressure readings, says Dr. Belardo, including:

Blood pressure readings also may depend on the method itself. According to Mustali Dohadwala, M.D., board-certified cardiologist and medical director of Heartsafe Boston, the following factors may impact accuracy:

The bottom line

Accurate blood pressure readings are critical because blood pressure is a key marker for cardiovascular health, says Dr. Del Conde Pozzi. "Inaccurate readings can result in misdiagnosis -- either underestimating or overestimating hypertension -- which can lead to incorrect treatment plans," Dr. Del Conde Pozzi says. Like a pilot needing precise information to ensure the safe operation of an airplane, individuals need accurate blood pressure readings to make informed decisions about their health and to avoid the potential dangers of untreated or poorly managed hypertension, he explains.

Specifically, improper arm position for recording blood pressure measurements may lead to overestimation in numbers, leading to the unnecessary introduction of prescription drugs and subsequent unexpected side effects, notes Dr. Dohadwala.

Many patients dismiss an elevated blood pressure reading in the office due to nerves, or having "white-coat" hypertension, says Brett Victor, M.D., F.A.C.C., cardiologist at Cardiology Consultants of Philadelphia. "This situation, while not uncommon, must be proven by several normal readings outside of the office." Good quality home monitors can be found at many pharmacies or online. Keeping a log of all blood pressure readings in your phone is an amazing set of data to share with your healthcare team, he adds.

When performing readings at home, Dr. Dohadwala says to remember that blood pressure does normally rise throughout the day: It peaks at midday and drops at nighttime while sleeping. "I would recommend [taking your measurement] sitting in a chair or at the bedside with feet flat on the ground, breathing normally. I would also advise measuring blood pressure no more than three to four times weekly, both in the morning and the evening," he says.

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