Consistency of blood pressure differences between the left and right arms

Background: It is unclear to what extent interarm blood pressure (BP) differences are reproducible vs the result of random error. The present study was designed to resolve this issue. Methods: We enrolled 147 consecutive patients from a hypertension clinic. Three sets of 3 BP readings were recorded, first using 2 oscillometric devices simultaneously in the 2 arms (set 1); next, 3 readings were taken sequentially for each arm using a standard mercury sphygmomanometer (set 2); finally, the readings as performed for set 1 were repeated (set 3). The protocol was repeated at a second visit for 91 patients. Results: Large interarm systolic BP differences were consistently seen in 2 patients with obstructive arterial disease. In the remaining patients, the systolic BP and the diastolic BP, respectively, were slightly higher in the right arm than in the left arm by 2 to 3 mm Hg and by 1 mm Hg for all 3 sets (P<.01 for all). For the systolic BP and the diastolic BP, respectively, the numbers of patients who had a mean interarm difference of more than 5 mm Hg were 11 (7.5%) and 4 (2.7%) across all 3 sets of readings. Among patients who repeated the test, none had a consistent interarm BP difference of more than 5 mm Hg across the 2 visits. Conclusions: The interarm BP difference was consistent only when obstructive arterial disease was present. Although BP in the right arm tended to be higher than in the left arm, clinically meaningful interarm differences were not reproducible in the absence of obstructive arterial disease and are attributable to random variation.