Have We Been Measuring Blood Pressure Incorrectly All Along?

Yesterday, it all seemed so simple. Put a blood pressure cuff on the patient’s arm closest to you. Measure pressure once. Use the JNC guidelines and treat to target.

But accumulating evidence seems to be rewriting every line of standard practice. Now there are home devices. Someone may ask, when should you use ambulatory blood pressure monitoring for decision-making? Which technique is most accurate and predictive?

A recent publication should shake us awake from any dogmatic slumbers.¹ If nothing else changes in contemporary debates, blood pressures in physicians’ offices—at a minimum—should be measured in both arms. Let’s look at why.

Early detection of peripheral vascular disease (PVD) leads to intensified efforts aimed at lowering risk factors. This should include strict blood pressure control. Right now, diagnosis of PVD at its earliest stages requires an ankle-brachial index (ABI)—a cumbersome tool in primary care practice. There may be another way to get the information needed.

Investigators associated a difference in systolic pressure between arms with vascular disease and mortality risk.^1,2 Overall, 25 studies (invasive and non-invasive) were incorporated into a meta-analysis. In the non-invasive studies (ie, those that did not use angiography to document PVD), a difference of 15 mm Hg in systolic pressure between arms was associated with PVD (relative risk [RR] of 2.5; 95% CI, 1.6 to 3.8; sensitivity, 15%; specificity, 96%) and pre-existing cerebrovascular disease (RR, 1.6; CI, 1.1 to 2.4; sensitivity, 8%; specificity, 93%), with associations as well for cardiovascular mortality (hazard ratio [HR], 1.7) and all cause mortality (HR, 1.6).

What do all these data tell us and— just as importantly—what don’t they tell us?

1. Blood pressure should routinely be taken in both arms on ambulatory visits.

2. Note that the 15 mm Hg difference has a high specificity, but a low sensitivity. The lack of a difference in systolic blood pressure between arms tells us little about the presence of PVD. ABI is still recommended for PVD screening in this instance. Remember that recent guidelines suggest routine ABI in primary care evaluation.³

Some things in the introduction were left hanging. Presently, ambulatory blood pressure monitoring is not standard of care in the United States. But that may be an evolving story. It is standard in other locations, including the United Kingdom.⁴ Data have been evaluating office blood pressure measurements. Office, and daytime/night-time ambulatory blood pressures in persons with chronic kidney disease (average glomerular filtration rate of 42.9 uL/min) were compared related to predicting risk.^5,6 Ambulatory blood pressures were not only the best predictors of hard endpoints, but office readings were not predictive at all.

This commentator does not have a crystal ball, but ambulatory blood pressures may be the next wave in blood pressure management. Until then, the cuff goes on both arms.