Objectives: To investigate whether there are inter-arm blood pressure differences 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 general practice.
Subjects: There were 237 patients presenting opportunistically for blood pressure 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 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.
Conclusions: 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.