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

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Abstract
To investigate whether there are inter-arm blood pressure differences that are of clinical importance to general practice. Pragmatic study with randomised order of use of left or right arm carried out in routine surgeries in an inner city and suburban general practice. There were 237 patients presenting opportunistically for blood pressure measurement to a nurse or general practitioner. 95% limits of agreement between measurements on the left and right arm and bias between arms. Large inter-arm blood pressure differences exist reflected in wide 95% limits of agreement; -16 mm Hg to 24 mm Hg for the right minus the left arm diastolic blood pressure. There is a small but statistically significant 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 difference of 10 mm Hg or greater for diastolic blood pressure occurred in 40% of subjects and a difference of 20 mm Hg or more for systolic blood pressure occurred in 23% of subjects. In a primary care setting blood pressure should be measured routinely in both arms. If one arm is to be preferred for pragmatic clinical purposes, then this should be the right arm.