Are you getting accurate blood pressure readings? Study reveals errors

Incorrect arm positioning during blood pressure checks may lead to inaccurate readings and potential misdiagnosis, according to a new study published in JAMA Internal Medicine on Monday, Oct. 7.

Researchers at Johns Hopkins University found that when a patient's arm is not properly supported during a blood pressure measurement, it can result in significantly higher systolic pressure readings — potentially by as much as 6.5 points.

The study compared blood pressure readings taken with patients' arms in three different positions: supported on a desk, resting on their lap, or hanging by their side. Results showed that unsupported arm positions led to notably higher readings than the recommended supported position.

Dr. Tammy Brady, senior author of the study and medical director of the pediatric hypertension program at Johns Hopkins Children's Center, said the findings were surprising.

"There was a chance that arm position was not important," Brady said. "One of my hopes is that this will help inform patients as to how to do this on their own and also to tell their health care provider the right way. Patients should be empowered to make sure the blood pressure measurement is accurate."

The research team recruited 133 adult participants, with 78% of them Black and 52% female, aged 18 to 80. Each participant had their blood pressure measured in all three arm positions, with the order randomized across six possible groups.

When participants' arms were hanging by their sides, systolic pressure readings averaged 6.5 points higher than when supported on a desk. Diastolic pressure was 4.4 points higher in the unsupported position.

Similarly, measurements taken with arms resting on participants' laps showed systolic pressure 3.9 points higher and diastolic pressure four points higher compared to the desk-supported position.

These differences could potentially lead to misdiagnosis of hypertension and unnecessary medication, experts warn.

Dr. Karyn Singer, assistant professor of medicine at New York University and assistant vice president of chronic disease and prevention at NYC Health + Hospitals, who was not involved in the study, called the findings "a piece of evidence that is really critical."

"Until now, it hasn't been clear how much arm position changes blood pressure readings," Singer said.

The American Heart Association recommends supporting patients' arms during blood pressure measurements to ensure accuracy. Additional guidelines include:

— Avoiding caffeine, exercise, and smoking for 30 minutes prior to the test

— Positioning the blood pressure cuff at mid-heart level

— Ensuring the patient's feet are flat on the floor with back supported

Nearly half of U.S. adults have high blood pressure, defined as readings consistently at or above 120/80 mm Hg. Untreated hypertension can increase the risk of serious cardiovascular conditions such as stroke and heart attack.

Dr. Matthew Tomey, a cardiologist at Mount Sinai Fuster Heart Hospital in New York City, who was not part of the study, said the findings support patients asking for proper measurement techniques.

"The differences found by the researchers can be enough to move someone from one blood pressure category to another," Tomey said.

Experts emphasize that patients should be aware of correct measurement techniques and advocate for themselves if they believe a reading may be inaccurate.

Dr. Megan Kamath, a cardiologist at UCLA Health who was not involved in the research, called it a "fascinating study" with important real-world implications.

"There is a pretty significant difference in blood pressure readings depending on arm position," Kamath said.

The potential consequences of inaccurate readings extend beyond misdiagnosis. According to Singer, patients unnecessarily prescribed blood pressure medication may experience side effects such as lightheadedness, dizziness, fatigue, and blurred vision.

Singer's main message for patients is to "Be aware of the proper blood pressure measuring technique and to advocate for themselves if they think the blood pressure reading is higher than they think it should be."

The study's findings underscore the importance of standardized blood pressure measurement techniques in clinical practice. As hypertension remains a significant public health concern, accurate diagnosis and appropriate treatment are crucial for managing cardiovascular risk.