Clothing and blood pressure measurement precision

We read with great interest the systematic review and meta-analysis recently published by Seguret et al. [1] regarding the effects of measuring blood pressure (BP) on a bare arm versus over a sleeve or below a rolled-up sleeve. The authors describe a nonsignificant mean 0.59 mmHg overestimation of SBP measured over ‘thin’ sleeves, a nonsignificant mean 1.10 mmHg overestimation of SBP measured over ‘thick’ sleeves, and a nonsignificant mean 2.76 mmHg overestimation of SBP measured below a rolled-up sleeve. From this, they conclude that BP measurement over a ‘thin’ sleeve does not have a significant clinical impact on SBP. However, we believe this conclusion misses the impact of measurement error on BP treatment at the patient level [2].

We present an ambulatory blood pressure monitoring (ABPM) report of a patient referred to our Hypertension Center to evaluate white-coat hypertension, whose ABPM cuff was unintentionally placed over an approximately 2 mm long-sleeve shirt. This report (see Fig. 1) shows an almost immediate drop in SBP after the patient repositioned the cuff directly on his bare skin at home for the remainder of the monitoring period. In fact, the average wake time blood pressure over his sleeve was 150/97 mmHg (17 measurements) versus 117/77 mmHg (33 measurements) over bare skin. In this case, the newly positioned cuff over bare skin was the difference between normotension and stage 2 hypertension. Indeed, his unwitnessed automated oscillometric blood pressure taken with the OMRON HEM907 the day after this ABPM was 126/73 mmHg, consistent with his daytime ABPM readings over bare skin.

FIGURE 1.

Sample ambulatory blood pressure monitor report (arrow highlights moving cuff to bare skin).

Although clothing may not introduce a differential measurement bias on average, it increases the variance of the measured bias. This has profound implications for patients at either tail of the distribution (i.e. a large negative or positive difference), as their hypertension status may be grossly misclassified as depicted in the case above.

We recognize that this single case may have other confounding factors; however, given the uphill battle to promote high-quality blood pressure measurements in clinic, we believe it is an instructive reminder that practitioners treat individuals (not populations), and that imprecise BP measure can misclassify patients’ hypertension, impacting their treatment and individual health. Although we wholeheartedly agree with the authors that following guideline-based proper BP measurement technique is not easy in a busy clinical practice, this extra effort is warranted to afford the most accurate and timely care to each patient we encounter.