Indirect blood pressure measurement for the diagnosis of hypertension in obese patients: A diagnostic accuracy review

The problem

The high prevalence of obese patients has led to many individuals not being suitable for blood pressure (BP) measurement with standard upper-arm cuffs. As a consequence, large upper-arm, forearm, and wrist cuffs are increasingly being used to diagnose hypertension. Current guidelines offer conflicting recommendation on which approach to take when a standard upper-arm cuff does not fit. The aim of this review was to determine the diagnostic accuracy of upper-arm, forearm, wrist and finger BP measurement compared to the reference standards of invasive, upper-arm (correctly fitting cuff) and ambulatory BP measurement for the diagnosis of hypertension in obese patients with a large arm circumference.

The approach

Medline, EMBASE, Cochrane, DARE, Medion and Trip databases weresearched. Cross-sectional, randomised and cohort studies of diagnostic test accuracy that compared any non-invasive BP tests (upper-arm, forearm, wrist, finger) with the reference standard (invasive BP pressure, correctly fitting upper-arm cuff, ambulatory BP monitoring) in primary care were included. Authors independently assessed included studies using QUADAS2 criteria. Hierarchical SROC modeling was used to obtain pooled estimates of sensitivity and specificity. Bland-Altman analyses were undertaken were individual patient data was available.

Findings

4037 potentially relevant studies were identified. 20 studies involving 26 different comparisons met the inclusion criteria. No studies satisfied all QUADAS2 criteria. Compared to the reference test of invasive BP a correctly fitting upper-arm BP cuff had sensitivity of 0.87 (0.79, 0.93) and specificity of 0.85 (0.64, 0.95). There was insufficient evidence to comment on how forearm, wrist and finger BP measurement performs in relation to invasive BP. Compared to the reference test of a correctly fitting upper-arm cuff, BP measurement at the wrist had a sensitivity 0.92 (0.64, 0.99) and specificity 0.92 (0.85, 0.87). Measurement with an incorrectly fitting standard cuff had a sensitivity of 0.73 (0.67, 0.78) and specificity of 0.76 (0.69, 0.82). Measurement at the forearm had a sensitivity of 0.84 (0.71, 0.92), specificity 0.75 (0.66,0.83). Bland-Altman analysis of individual patient data from three studies comparing wrist and upper-arm BP showed a mean difference of 0.46 mmHg for systolic BP measurement and 2.2 mmHg for diastolic BP measurement.

Consequences

BP measurement with a correctly fitting upper-arm cuff is sufficiently sensitive and specific to diagnose hypertension in obese patients with a large upper-arm circumference. If a correctly fitting upper-arm cuff cannot be applied an incorrectly fitting standard size cuff should not be used. Instead, BP measurement at the wrist should be considered in preference to measurement at the forearm or finger. There was good agreement between wrist and upper-arm BP measurement with a correctly fitting cuff. The mean difference falls within the BHS standard (+/- 3mmHg) and within the limits for clinically relevant difference (+/-5mmHg).

Credits

• Greg Irving, Garswood Surgery, St.Helens, UK
• John Holden, University of Oxford, Oxford, UK
• Richard McManus