For accurate readings, the angle matters

How you position your arm during a blood pressure check could potentially determine whether your doctor properly diagnoses and treats your hypertension.

That conclusion comes from a study in which researchers at UC San Diego placed patients’ arms in slightly exaggerated positions. With the arm straight and parallel to the body, blood pressure readings can be up to 10% higher than when the elbow is bent at a right angle to the body at the level of the heart, researchers found. The ideal position falls between those extremes, with the arm at heart level and the elbow slightly flexed.

Dr. David Guss, director of emergency room services at UC San Diego, oversaw the study of 100 emergency room patients with signs of cardiovascular problems. Two medical students took readings from the left arm when the patients were standing, sitting or lying down, first with the arm perpendicular to the body, then with the arm parallel to the body.

Among patients who were seated, readings taken in the perpendicular position showed hypertension in 22%. Readings from arms held parallel showed hypertension in 41%. In every body position, the upper (systolic) and lower (diastolic) blood pressure readings were from 8.8 to 14.4 points lower with a perpendicular arm than with a parallel arm. Previous studies have found that 73% of health-care workers don’t put patients’ arms in the proper position. “The take-home message from this study is that arm position is important and that at the very least, it should be consistent from measurement to measurement,” said Guss.