Common arm positioning during blood pressure (BP) screenings may significantly overestimate BP measurements, leading to misdiagnosis of hypertension, according to a study led by Johns Hopkins Medicine researchers.

The study was published Oct. 7 in the journal JAMA Internal Medicine. The researchers analyzed the effects of three different arm positionings on BP measurements: with the arm on a table, supported in the lap, and hanging unsupported at the side of the body. The study found that systolic blood pressure (the upper limit of BP readings) was overestimated by an average of nearly 4 mmHg when the arm was in the lap, and by nearly 7 mmHg when the arm was hanging unsupported.

Importance of arm position for blood pressure measurement

"Arm position has an important impact on the accuracy of blood pressure measurement," said Dr. Tammy Brady, senior author of the study and associate director of clinical research in pediatrics at the Johns Hopkins University School of Medicine. The study further emphasizes the need to follow clinical guidelines, that is, to ensure that the arm is firmly supported when measuring blood pressure, such as on a table or other stable surface.

According to the American Heart Association (AHA), nearly half of adults in the United States have high blood pressure, that is, systolic blood pressure (upper limit) ≥ 130 mmHg or diastolic blood pressure (lower limit) ≥ 80 mmHg. If high blood pressure is not effectively controlled, it will greatly increase the risk of cardiovascular diseases such as stroke and heart attack. Because high blood pressure usually has no obvious symptoms, early screening and frequent monitoring during routine physical examinations are important means of managing high blood pressure. In most cases, blood pressure levels can be effectively controlled through lifestyle adjustments (such as weight loss, healthy diet, exercise) and drug treatment.

Research methods and key findings

The latest AHA clinical practice guidelines emphasize that accurate blood pressure measurement requires the following requirements: choose the right blood pressure cuff size, ensure that the back is supported, feet flat on the ground and legs are not crossed, and the arm should be placed on a table or desk so that the midpoint of the cuff is at the same level as the heart.

Despite the clear recommendations, researchers pointed out that there are still many irregularities in clinical practice. For example, many patients sit on the examination bed during the examination, their arms lack support, or their arms are supported by medical staff or patients themselves. In this study, researchers randomly recruited 133 adults aged 18 to 80 years to participate in the test between August 9, 2022 and June 1, 2023, of whom 78% were black and 52% were women.

Participants were randomly assigned to six different test groups to test the effects of different arm positions on blood pressure measurement. All measurements were performed in a quiet and private environment, and subjects were asked to avoid talking to researchers or using mobile phones.

The study found that compared with the standard desktop support, the common clinical method of measuring blood pressure with the arm on the leg or hanging on the side of the body will result in significantly higher blood pressure values. Specifically, the systolic blood pressure measured with the arm on the leg is 3.9 mmHg higher than the standard measurement value, and the diastolic blood pressure is 4.0 mmHg higher; when the arm is suspended without support, the systolic blood pressure is 6.5 mmHg higher and the diastolic blood pressure is 4.4 mmHg higher.

Impact of overestimating blood pressure and clinical recommendations

"If blood pressure is not measured correctly, each systolic blood pressure measurement will be 6.5 mmHg higher, which means that a person's systolic blood pressure may change from 123 mmHg to 130 mmHg, or from 133 mmHg to 140 mmHg - and above 140 mmHg is considered stage 2 hypertension," explained Sherry Liu, one of the study authors and coordinator of epidemiological research at the Johns Hopkins Bloomberg School of Public Health.

Dr. Brady said the findings highlight that clinicians should pay more attention to measurement standards, and patients should also actively ask to follow the best measurement methods when measuring in medical settings or at home.