54 million US adults may be misdiagnosed with high BP based on bad readings. Many people may be surprised to learn the proper procedure for taking a blood pressure reading—because of how different it is from what happens during their doctor's appointments.

In the study, published Monday in JAMA Internal Medicine, researchers compared blood pressure readings of 133 adults who held their arms in three different positions: resting on the lap, leaning on a surface and hanging by their side.

Two common arm positions for getting a blood pressure reading can lead to misdiagnoses of hypertension, new research finds.