A difference in blood pressure readings between arms can be seen in congenital heart disease, aortic dissection, peripheral vascular disease, and unilateral neuromuscular abnormalities. In the absence of these conditions, any discrepancy is small (mean difference: 5 mm Hg and 4 mm Hg for systolic and diastolic blood pressure, respectively).1 About 20% of patients in primary care or secondary care have a between arm blood pressure difference of 10 mm Hg or more and 4% have a difference of 20 mm Hg or more.2 Although such a difference in blood pressure is thought to be a marker of atherosclerosis,3 its clinical significance is not fully understood. In a linked research study (doi:10.1136/bmj.e1327),4 and in a recent meta-analysis,5 Clark and colleagues provide additional evidence on the diagnostic and prognostic relevance of this phenomenon.

In their meta-analysis of cross sectional studies,5 Clark and colleagues reported that a between arm blood pressure difference of 15 mm Hg or more was associated with peripheral vascular disease (sensitivity 15% and specificity 96%) and with cerebrovascular disease (sensitivity 8% and specificity 93%), but not with coronary artery disease. A difference of 10 mm …