Randomised diagnostic accuracy study of a fully automated portable device for diagnosing peripheral arterial disease by measuring the toe-brachial index

Abstract

Objective: To assess the accuracy of a fully automated portable device (APD) for diagnosing peripheral arterial disease (PAD) by measuring the toe-brachial index (TBI) and using mercury-in-silastic, strain-gauge plethysmography (SGP) as reference.

Design: Prospective, randomised, double-blinded diagnostic accuracy study.

Materials and methods: A total of 204 consecutive patients with known or suspected PAD were randomly assigned to measurement of TBI by the portable device followed by the SGP technique or the opposite sequence. Finally, ankle-brachial index (ABI) was assessed by SGP.

Results: The APD showed a sensitivity of 98.8%, a specificity of 61.0%, a positive predictive value of 91.0% and a negative predictive value of 92.6% for detecting PAD compared to a full SGP test comprised of ABI and TBI. According to the SGP test, 35 patients (17.2%) had an ABI > 0.90 but a TBI < 0.70. Correlation analysis of the absolute toe pressures by the two methods showed an intraclass correlation coefficient of 0.937 (95% confidence interval (CI) 0.887-0.962) for right toe pressures and 0.939 (95% CI 0.908-0.958) for the left toe pressures.

Conclusions: The APD showed excellent diagnostic test characteristics for detecting PAD compared to SGP. Furthermore, the APD had a good correlation in absolute toe pressures with SGP.