Tammy Brady and colleagues at Johns Hopkins University conducted clinical trials and found that incorrect arm positioning during blood pressure measurements can overestimate blood pressure readings by more than six millimeters of mercury. The ARMS randomized crossover trial involved 133 volunteers (53 percent women) from Baltimore, aged 18–80 (mean 57). Thirty-six percent of participants had blood pressure of 130 mmHg or higher, and 41 percent had a body mass index of 30 kilograms per square meter or higher. They were randomly assigned to have their blood pressure measured with their arm resting on a table with the cuff at heart level (as recommended by clinical guidelines), resting on their lap, or hanging freely without support. To account for natural blood pressure variability, everyone then had their blood pressure measured again with their arm resting on the table. A report on the work was published in the journal JAMA Internal Medicine.
It turned out that when measuring with the arm resting on the lap, systolic pressure readings were overestimated by an average of 3.9 mmHg, and diastolic pressure by 4.0 mmHg. When measuring with the arm unsupported, these readings were 6.5 and 4.4 mmHg, respectively. When stratifying the results by the presence of hypertension, age, obesity, and medical attention in the previous year, the identified patterns persisted across all subgroups. Thus, incorrect arm positioning during blood pressure measurement, which is common in practice, can lead to misdiagnosis and overestimation of the severity of hypertension.
