Differences between right and left arm blood pressures in the elderly.

Recommendations vary on whether blood pressures should be measured in the right or in the left arm because no frequency distributions for a pressure difference between the arms exist. We took a total of 12 blood pressure determinations in both arms of 174 elderly persons and analyzed the data by a least-squares components of variance method. The mean difference between the arms (right minus left) was 0.93 mm of mercury for systole and 0.70 mm of mercury for diastole. For systole the proportion of persons having arm pressure differences exceeding 10 mm of mercury is 1.4% and that exceeding 7.5 mm of mercury is 6.5%. For most people, the pressure difference between the arms is small.