This suggests that not consistently having your arm positioned and supported appropriately during a blood pressure reading might result in a misdiagnosis of high blood pressure, which some experts worry could possibly lead to unnecessary treatment.
The study, published Monday in the journal JAMA Internal Medicine, found that having your arm resting in the lap during a blood pressure reading can lead to an overestimated systolic blood pressure measurement by 3.9 mm Hg and overestimated diastolic reading by 4 mm Hg.
And having your arm hang by your side can lead to an overestimated systolic reading by 6.5 mm Hg and overestimated diastolic reading by 4.4 mm Hg.
A person is considered as having high blood pressure or hypertension if they have consistent readings of 130/80 or higher.
"Health care providers need to be reminded about the importance of taking the time to do these steps properly," said the study's senior author Dr. Tammy Brady, who serves as vice chair for clinical research in the department of pediatrics at the Johns Hopkins University School of Medicine. "I just hope that it raises awareness regarding how important things like arm position are to blood pressure measurement accuracy."
She added: "I also hope this study educates patients, empowering them to advocate for proper measurement when they're in a clinic setting. But also, because so many patients rely on home blood pressure measurements for hypertension diagnosis, evaluation, and treatment, I hope this educates them on how to properly position their arms because our findings absolutely extend to measurements in the home."
The Johns Hopkins University researchers recruited 133 adults from Baltimore, Maryland for the study.
The adults, ages 18 to 80, were randomly assigned to have their blood pressure measured while their arms were positioned in three different ways: supported on a desk, as is the recommended standard practice; supported on their lap; or hanging by their side, unsupported.
Each study participant underwent a total of 12 blood pressure measurements with their arms in each of those various positions. When their arms were supported on a desk as recommended by the standard clinical guidelines, the average of their blood pressure reading was 126/74, the researchers found.
But 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 of their readings was 133/78.
Researchers were surprised how much difference the positions made.
The researchers wrote in the study that the "latest clinical practice guidelines emphasize several key steps for accurate measurement," including:
- Wear the appropriate cuff size
- Have your back supported
- Keep feet flat on the floor with legs uncrossed
- Have the appropriate arm position: the cuff should be positioned at heart level with the arm supported on a desk or table
An improperly sized blood pressure cuff can distort blood pressure readings taken by automated blood pressure devices.
Patients should also take steps before they have their blood pressure checked. No smoking, no caffeine, no alcohol, and no arguments in the 30 minutes before you take your blood pressure.
Sit in the chair, get in the right position, and for five minutes, relax. You don't talk, rest your arm comfortably, sit upright with your back straight, keep your legs uncrossed and your feet flat on the floor.
The cuff should be against your arm, not over clothes. And don't talk while the reading is being taken.
Because people often feel more calm and comfortable at home, "what we're finding now is studies suggest that blood pressures measured at home are a better indicator of your usual blood pressure than blood pressures measured in the office," Dr. Gail Adler of Brigham and Womens said.