A study examined three common arm positions during blood pressure screenings and found that two of them significantly overestimated results, potentially leading to misdiagnosis.
Summary: A study led by Johns Hopkins Medicine found that commonly used arm positions during blood pressure screenings can significantly overestimate readings, potentially leading to a misdiagnosis of hypertension. Researchers tested three different arm positions—supported on a desk, supported on a lap, and unsupported at the side—and discovered that incorrect arm positioning can elevate systolic and diastolic pressure readings by up to 7 mmHg.
Key Takeaways:
- Arm Position Impacts Blood Pressure Accuracy: The study found that supporting the arm on a desk resulted in more accurate readings, while lap support overestimated systolic pressure by 3.9 mmHg, and an unsupported arm hanging at the side overestimated systolic pressure by 6.5 mmHg.
- Risk of Hypertension Misdiagnosis: These overestimations could lead to false hypertension diagnoses, with differences between supported and unsupported arm measurements potentially marking the threshold between normal blood pressure and stage 2 hypertension.
- Need for Adherence to Guidelines: The findings highlight the importance of following clinical guidelines that recommend firm arm support to ensure accurate blood pressure readings, stressing that both clinicians and patients must be aware of proper arm positioning during tests.
A study led by Johns Hopkins Medicine researchers concludes that commonly used ways of positioning the patient’s arm during blood pressure screenings can substantially overestimate test results and may lead to a misdiagnosis of hypertension.
In a report on the study, which was published in JAMA Internal Medicine, investigators examined the effects of three different arm positions: an arm supported on a desk, arm supported on a lap, and an unsupported arm hanging at the patient’s side. Researchers found that lap support overestimated systolic pressure by nearly 4 mmHg, and an unsupported arm hanging at the side overestimated systolic pressure by nearly 7 mmHg.
The findings confirm that arm position makes a “huge difference” when it comes to an accurate blood pressure measurement, says Tammy Brady, MD, PhD, vice chair for clinical research in the Department of Pediatrics at the Johns Hopkins University School of Medicine, medical director of the pediatric hypertension program at Johns Hopkins Children’s Center, deputy director of the Welch Center for Prevention, Epidemiology, and Clinical Research, and senior author of the study, in a release.
They also underscore the importance of adhering to clinical guidelines calling for firm support on a desk or other surface when measuring blood pressure, the investigators add.
The latest clinical practice guidelines from the American Heart Association emphasize several key steps for an accurate measurement, including appropriate cuff size, back support, feet flat on the floor with legs uncrossed, and an appropriate arm position, in which the middle of an adjustable blood pressure cuff is positioned at mid-heart level on an arm supported on a desk or table.
Despite these recommendations, the researchers say blood pressure is too often measured with patients seated on an exam table without any, or inadequate, arm support. In some cases, a clinician holds the arm, or the patient holds an arm in their lap.
Investigating Impact of Arm Position
In the new Johns Hopkins study, the researchers recruited 133 adult participants (78% Black, 52% female) between Aug 9, 2022, and June 1, 2023. Study participants, who ranged from age 18 to 80, were sorted at random into one of six possible groups that differed by order of the three seated arm positions. Measurements were taken during a single visit between 9 am and 6 pm.
Before blood pressure measures were taken, all participants first emptied their bladders and then walked for two minutes to mimic a typical clinical scenario in which people walk into a clinic or office before screening takes place. They then underwent a five-minute, seated rest period with their backs and feet supported. Each person, wearing an upper arm blood pressure cuff selected and sized based on their upper arm size, had three sets of triplicate measurements taken with a digital blood pressure device 30 seconds apart.
Upon completion of each set of three measurements, the cuff was removed, and participants walked for two minutes and rested for five minutes. In the same visit, they then underwent a fourth set of triplicate measurements with their arm supported on a desk, a set used to account for well-known variations in blood pressure readings. All of the measurements were conducted in a quiet and private space, and participants were asked not to talk to researchers or use their phones during the screening.
Overestimating Blood Pressure
Researchers found that blood pressure measurements obtained with arm positions frequently used in clinical practice—an arm on the lap or unsupported at the side—were markedly higher than those obtained when the arm was supported on a desk, the standard, recommended arm position. Supporting the arm on the lap overestimated systolic blood pressure—the top number of a reading, or the force of blood flow when pumped out of the heart, by 3.9 mmHg and diastolic blood pressure—the bottom number, or the pressure in the arteries when the heart rests between beats, by 4.0 mmHg.
An unsupported arm at the side overestimated systolic by 6.5 mmHg and diastolic by 4.4 mmHg.
“If you are consistently measuring blood pressure with an unsupported arm, and that gives you an overestimated [blood pressure] of 6.5 mmHg, that’s a potential difference between a systolic [blood pressure] of 123 and 130, or 133 and 140—which is considered stage 2 hypertension,” says Sherry Liu, MHS, an epidemiology research coordinator at the Welch Center for Prevention, Epidemiology, and Clinical Research, Department of Epidemiology, at Johns Hopkins Bloomberg School of Public Health and study author.
Investigators caution that their study results may only apply during screenings with automated blood pressure devices and may not apply to readings done with other blood pressure devices.
However, Brady says the findings suggest that clinicians need to pay better attention to best practice guidelines and that patients “must advocate for themselves in the clinical setting and when measuring their [blood pressure] at home.”
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