How do you get accurate blood pressure readings. Certain arm positions commonly used for blood pressure checks may lead to inaccurate results.
A new study found that having your arm in the wrong position during blood pressure checks — either at home or the doctor’s office — can result in readings “markedly higher” than when your arm is in the recommended position: appropriately supported on a table with the middle of the cuff positioned at heart level.
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.
Study on Accurate Blood Pressure Readings
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.
Blood pressure is measured in units of millimeters of mercury or mm Hg, which consists of two numbers – the upper or systolic reading and the lower or diastolic reading. 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 and medical director of the pediatric hypertension program at Johns Hopkins Children’s Center.
“I just hope that it raises awareness regarding how important things like arm position are to blood pressure measurement accuracy,” Brady said about the study.
“I also hope this study educates patients, empowering them to advocate for proper measurement when they’re in a clinic setting,” she said. “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.”
How the Research Was Conducted
• The researchers, from Johns Hopkins University, recruited 133 adults from Baltimore, Maryland, between August 2022 and June 2023, to participate in 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.
• Among the participants, 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.
Analysis of Study Results
“I did not expect there to be that much of a difference when the arms were placed in the two alternative positions. We tested those positions because those are the positions that most people have their blood pressure measured, according to data and personal observations,” Brady said. “We thought there’d be a difference, but I was surprised by how much of a difference there was.”
The researchers wrote that there are several physiological reasons why blood pressure measurements could be erroneously higher when the arm is not adequately positioned or supported. A greater vertical distance between the heart and where the cuff is placed can increase hydrostatic pressure in the arteries, or the pressure of the blood against the wall, due to gravity’s pull, leading to an overestimation of blood pressure. And an unsupported arm can lead to the muscle contracting, which may cause an increase in blood pressure.
How to check blood pressure accurately
The new study findings are consistent with some separate previous research that has shown unsupported arm positions or the arm being positioned below heart level can overestimate a blood pressure reading.
“This is seen in participants with all levels of blood pressure, but more pronounced in participants with elevated blood pressure. These are important findings because we diagnose and treat hypertension based on blood pressure readings, and these readings need to be accurate,” Davis said in the email.
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.
Wearing the appropriate cuff size is key because an improperly sized blood pressure cuff can distort blood pressure readings taken by automated blood pressure devices. One study, published last year in the journal JAMA Internal Medicine, found that using standard, regular-sized blood pressure cuffs resulted in “strikingly inaccurate” readings if a patient required differently sized ones, particularly for participants who fit larger cuffs.
There are some steps people should take before they have their blood pressure checked, said Dr. Gail Adler, a cardiovascular endocrinologist and co-specialist in the Hypertension Clinic at Brigham and Women’s Hospital, who was not involved in the new study.
“In the 30 minutes before you take your blood pressure, you want no smoking, no exercise, no caffeine, no alcohol, and … no major arguments. Don’t be psychologically stressed,” Adler said.
“Then what you want to do is you want to sit in the chair, get in the right position, and for five minutes, you relax, you don’t talk, you rest your arm comfortably, you sit upright with your back straight, you keep your legs uncrossed and your feet flat on the floor.
Make sure you don’t have to pee, if you have to pee or urinate, that’s going to raise your blood pressure,” she said. “And you’re not supposed to talk when you take your blood pressure, and the cuff should be against your arm. So you don’t want to put it over clothes.”
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,” Adler said.
“Anecdotally, I think all of us on the study team have started to pay more attention to how our blood pressures are being measured. I’ve certainly paid attention to how my kids’ blood pressures are being measured,” Brady said.
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