Improper arm position results in significantly higher blood pressure readings

Patients placing their arm on their lap or by their side when having blood pressure measured resulted in substantial overestimations of readings compared with placement on a desk, especially among individuals with hypertension, a randomized crossover trial found.

To determine the effect of different arm positions on blood pressure readings, 133 participants (mean age, 57 years; 53% female) were randomly assigned to blood pressure measurements with the arm positioned in three ways: supported on a desk, hand supported on lap, and arm unsupported at the side. Guidelines for blood pressure measurement recommend that the arm be supported on a desk with the midcuff positioned at heart level, but nonstandard positions are still used in clinical practice, the study authors explained. Primary outcomes included difference in differences in mean systolic blood pressure (SBP) and diastolic blood pressure (DBP) between the reference blood pressure (supported on a desk) and the other two arm positions. Findings were published by JAMA Internal Medicine on Oct. 7.

Forty-eight 48 participants had an SBP of 130 mm Hg or higher, and 55 participants had a body mass index of 30 kg/m² or greater. Lap and side positions resulted in statistically significantly higher blood pressure readings than desk positions among all patients. SBP was overestimated by 3.9 mm Hg (95% CI, 2.5 to 5.2 mm Hg) in the lap position and 6.5 mm Hg (95% CI, 5.1 to 7.9 mm Hg) in the side position, while overestimations of DBP were 4.0 mm Hg (95% CI, 3.1 to 5.0 mm Hg) and 4.4 mm Hg (95% CI, 3.4 to 5.4 mm Hg), respectively. Patterns were generally consistent across patient subgroups, but there was a statistically significantly larger difference in lap versus desk blood pressures among participants who had not received medical care within the last year versus those who had. In addition, SBP was overestimated by approximately 9 mm Hg in patients with hypertension when their arm was positioned at their side.

Limitations to the study include relatively small sample sizes and uncertainty as to whether results can be generalized to settings where different blood pressure devices are used.

Using data from the National Health and Nutrition Examination Survey, the researchers estimated that improper arm position would result in 16% of U.S. adults, or 40 million people, being misclassified as hypertensive when an SBP cutoff of 140 mm Hg and higher was used. That estimate rose to 22% (54 million individuals) for an SBP cutoff of 130 mm Hg and higher.

“Although the error in SBP with the arm supported in the lap was less striking in magnitude than when the arm was unsupported at the side (approximately 4 mm Hg vs approximately 7 mm Hg), [blood pressure] readings in either position were sufficiently high to raise concerns for overdiagnosis and overtreatment,” the authors wrote.