A study of inter-arm blood pressure differences in primary care

Objectives: To investigate whether there are inter-arm blood pressure diffe rences that are of clinical importance to general practice. Design and setting: Pragmatic study with randomised order of use of left or right arm carried out in routine surgeries in an inner city and suburban g eneral practice. Subjects: There were 237 patients presenting opportunistically for blood pr essure measurement to a nurse or general practitioner. Main outcome measures: 95% limits of agreement between measurements on the left and right arm and bias between arms. Results., Large inter-arm blood pressure differences exist reflected in wid e 95% limits of agreement; -16 mm Hg to 24 mm Hg for the right minus the le ft arm diastolic blood pressure. There is a small but statistically signifi cant bias to the right arm blood pressure measuring higher than the left (3 .7 mm Hg diastolic, 2.4 to 5 mm Hg 95% confidence intervals). An interarm d ifference of 10 mm Hg or greater for diastolic blood pressure occurred in 4 0% of subjects and a difference of 20 mm Hg or more for systolic blood pres sure occurred in 23% of subjects. Conclusions: In a primary care setting blood pressure should be measured ro utinely in both arms. If one arm is to be preferred for pragmatic clinical purposes, then this should be the right arm.