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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 Hg or more was associated only with peripheral vascular disease (sensitivity 32% and specificity 91%). 5 The overall low sensitivity and high specificity suggest that the measurement of blood pressure in both arms is not a good screening test for asymptomatic peripheral vascular disease.
On the basis of these prevalence data, it might seem sensible to examine whether, as a marker of asymptomatic peripheral vascular disease of the upper extremities, a difference in blood pressure between arms predicts future cardiovascular events and mortality. Although extensive data show an association between peripheral vascular disease of the lower extremities and both all cause mortality and mortality from cardiovascular disease, 6 little evidence exists for the prognostic value of between arm blood pressure differences. 4 7 The authors of a prospective study of 1872 community dwelling adults and patients evaluated for peripheral vascular disease of the...