Blood pressure measurement: a call to arms

Our hard-pressed workforce may view the linked article by Clark and colleagues with a mixture of interest and trepidation.1 Their systematic review builds on earlier work to estimate the prevalence of inter-arm difference (IAD) in blood pressure (BP) in populations relevant to primary care. Pooled estimates of prevalence for systolic IAD of ≥10 mmHg were 11% in patients with hypertension, 7% for those with diabetes, and just under 4% in the general adult population. GPs are masters of distilling from their training and experience the shortest route to a clinical decision. This does not generally involve checking BP in both arms.1 Yet, paradoxically, this new evidence could reduce workload, because accurate identification of IAD in a minority of patients, and the exclusion of this condition in the majority, might inform a more rational and streamlined approach to blood pressure management in both groups. Many studies investigating IAD have used sequential measurements, that is, using the same manometer in first one then the other arm. An important finding in Clark and colleagues’ systematic review was that prevalence of IAD is overestimated threefold by sequential measurement compared with the repeated simultaneous blood pressure measurement protocol from which the headline prevalences were derived.1 Recommendations for simultaneous measurement of IAD may seem at odds with the consistent finding of a relationship between an apparent IAD — using the sequential approach — and cardiovascular events.1,2 Interestingly, the work of Sheppard and colleagues suggests that variation across consecutive blood pressure measurements during a single clinic visit is neither random nor meaningless. They show that a large decrease in blood pressure across multiple readings is predictive of the white-coat effect (lower out-of-office pressure), …