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If you’ve ever had a high blood pressure reading, there’s a chance your arm position skewed the result. A study out this week finds that two common positions for taking blood pressure can often lead to overestimates. It’s possible these flubs may lead to people getting mistakenly diagnosed with hypertension, the researchers say.
Blood pressure is one of the most important metrics for evaluating a person’s overall health. Chronically high blood pressure, or hypertension, is known to raise the risk of heart disease and stroke, two major leading causes of death, and high blood pressure can be an indicator of other health issues such as type 2 diabetes. But these new findings suggest that there is a glaring blind spot in how doctors and patients at home are conducting this essential test.
Researchers at Johns Hopkins performed the study, published Monday in JAMA Internal Medicine. They recruited 133 adults between the ages of 18 and 80 to take part in a crossover randomized trial, meaning that the volunteers all participated in the different conditions of the study (but in randomized order). The participants had their blood pressure taken via their arm in three ways: the widely recommended position of supporting their arm on a desk, having their arm dangling by the side unsupported, and having their hand rested on their lap.
Compared to the gold standard method of having the arm supported on a desk, the other two methods consistently resulted in higher blood pressure readings, the researchers found. On average, using a lap-rested arm led to a systolic blood pressure measurement (the top number) 3.9 mm Hg higher than normal and a diastolic measurement (the bottom number) 4 mm Hg higher. Using an unsupported arm led to a systolic measurement 6.5 mm Hg higher than normal and a diastolic reading 4.4 mm Hg higher.
For context, a blood pressure reading of 130/80 is the threshold for hypertension. And the researchers say that doctors relying on these two methods could certainly misdiagnose some of their patients as having high blood pressure. Similar misreadings could also happen with patients taking their blood pressure at home.
“This crossover randomized clinical trial showed that commonly used arm positions (lap or side) resulted in substantial overestimation of BP readings and may lead to misdiagnosis and overestimation of hypertension,” they wrote.
Some previous research has found that subtle factors like arm positioning or support can affect blood pressure measurements, but this study appears to be one of the first randomized trials to try quantifying the difference. Other research has suggested that even the location of a test can affect people’s readings. One such well-known phenomenon is “white coat hypertension,” which is when people consistently have higher blood pressure readings at a doctor’s office than at home, possibly due to anxiety (that said, people with white coat hypertension may still have a higher cardiovascular risk than someone with normal blood pressure at all times)
The researchers hope that their findings can help other doctors and patients.
“Health care providers need to be reminded about the importance of taking the time to do these steps properly,” senior researcher Tammy Brady, medical director of the pediatric hypertension program at Johns Hopkins Children’s Center, told CNN. “I also hope this study educates patients, empowering them to advocate for proper measurement when they’re in a clinic setting.”
