Accuracy of Cuff-Measured Blood Pressure
What is the accuracy of cuff blood pressure (BP) and the consequent effect on BP classification compared with intra-arterial BP reference standards?
Three individual participant data meta-analyses were conducted among studies (from the 1950s to 2016) that measured intra-arterial aortic BP, intra-arterial brachial BP, and cuff BP.
A total of 74 studies with 3,073 participants were included. Intra-arterial brachial systolic BP (SBP) was higher than aortic values (8.0 mm Hg; 95% confidence interval, 5.9-10.1 mm Hg; p < 0.0001) and intra-arterial brachial diastolic BP was lower than aortic values (-1.0 mm Hg; -2.0 to -0.1 mm Hg; p = 0.038). Cuff BP underestimated intra-arterial brachial SBP (-5.7 mm Hg; -8.0 to -3.5 mm Hg; p < 0.0001), but overestimated intra-arterial diastolic BP (5.5 mm Hg; 3.5-7.5 mm Hg; p < 0.0001). Cuff and intra-arterial aortic SBP showed a small mean difference (0.3 mm Hg; -1.5 to 2.1 mm Hg; p = 0.77), but poor agreement (mean absolute difference, 8.0 mm Hg; 7.1-8.9 mm Hg). Concordance between BP classification using the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure cuff BP (normal, pre-HTN, and HTN stages 1 and 2) compared with intra-arterial brachial BP was 60%, 50%, 53%, and 80%, and using intra-arterial aortic BP was 79%, 57%, 52%, and 76%, respectively.
Cuff BP has variable accuracy for measuring either brachial or aortic intra-arterial BP, and this adversely influences correct BP classification. These findings indicate that stronger accuracy standards for BP devices may improve cardiovascular risk management.
The authors state an inaccuracy of 5 mm Hg is estimated to result in the misclassification of BP of 48 million people each year in the United States alone (21 million underestimated BP, 27 million overestimated BP). While this is true, much more important than the error comparing the cuff with intra-arterial is the too often reliance on the standard office cuff pressure rather than the automatic cuff pressure over 6 minutes, am and pm home cuff pressures, and 24-hour ambulatory BP, each of which has been shown to be superior in clinical drug trials and prediction of outcome in hypertension.
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