Inter-arm differences in blood pressure: when are they clinically significant?

OBJECTIVE : To determine whether there is significant disparity in blood pressure between the two arms. DESIGN : Prospective, observational study. SETTING : One general hospital in Birmingham, England. PARTICIPANTS : Four hundred participants [age 56.3 +/- 19.7 years (mean +/- SD), 50% male] were recruited from staff and patients. Simultaneous bilateral blood pressure measurements were obtained using Omron HEM-705CP automated oscillatory devices; with two measurements taken in each arm. MAIN OUTCOME MEASURES : Mean inter-arm blood pressure differences and frequency of clinically important disparities. RESULTS : Mean +/- SD inter-arm differences in systolic and diastolic blood pressure were 1.81 +/- 8.6 mmHg and -0.23 +/- 8.3 mmHg, respectively. The analogous figures for mean +/- SD absolute differences were 6.32 +/- 6.12 mmHg and 5.06 +/- 6.57 mmHg, respectively. Significant differences were present between the mean right and left arm systolic blood pressure [t(399) = 4.20, P <0.0001], and the mean absolute difference for both systolic [t(399) = 20.65; P <0.0001] and diastolic [t(399) = 15.39; P <0.0001] blood pressure. The variation in mean inter-arm blood pressure was unrelated to age, sex, ethnicity, arm circumference, handedness, being hypertensive, diabetic, or previous history of cardiovascular disease. Clinically significant inter-arm differences in systolic blood pressure of > 10 and > 20 mmHg were found in 20 and 3.5%, respectively; diastolic differences of > 10 and > 20 mmHg were present in 11 and 3.5%, respectively. Age was the only significant predictor of clinically significant variations in inter-arm blood pressures and mean absolute blood pressure differences. CONCLUSIONS : Significant differences in mean inter-arm systolic blood pressure, and mean absolute inter-arm systolic and diastolic blood pressure are present. This emphasizes the importance of measuring blood pressure in both arms initially to prevent this misdiagnosis of hypertension, due to normal differences in blood pressure between the arms.