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

AbstractObjectiveTo 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.DesignProspective, randomised, double-blinded diagnostic accuracy study.Materials and methodsA 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.ResultsThe 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.ConclusionsThe 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

The toe-brachial index in the diagnosis of peripheral arterial disease

BackgroundPeripheral arterial disease (PAD) can be diagnosed noninvasively by segmental blood pressure measurement and calculating an ankle-brachial index (ABI) or toe-brachial index (TBI). The ABI is known to be unreliable in patients with vascular stiffness and fails to detect the early phase of arteriosclerotic development. The toe vessels are less susceptible to vessel stiffness, which makes the TBI useful. However, the diagnostic limits used in guidelines, clinical settings, and experimental studies vary substantially. This review provides an overview of the evidence supporting the clinical use of the TBI.MethodsA review of the literature identified studies reporting the use of the TBI regarding guideline recommendations, normal populations, correlations to angiographic findings, and prognostic implications.ResultsEight studies conducted in a normal population were identified, of which only one study used imaging techniques to rule out arterial stenosis. A reference value of 0.71 was estimated as the lowest limit of normal based on the weighted average in studies with preheating of the limbs. A further seven studies showed correlations of the TBI with angiographic findings. The TBI had a sensitivity of 90% to 100% and a specificity of 65% to 100% for the detection of vessel stenosis. Few studies investigated the value of the TBI as a prognostic marker for cardiovascular mortality and morbidity, and no firm conclusions could be made. Studies have, however, shown correlation between the TBI and comorbidities such as kidney disease, diabetes, and microvasculature disease.ConclusionsIn contrast to the well-defined and evidence-based limits of the ABI, the diagnostic criteria for a pathologic TBI remain ambiguous. Although several guidelines and reviews of PAD diagnostics recommend a TBI <0.70 as cutoff, it is not strictly evidence-based. The current literature is not sufficient to conclude a specific cutoff as diagnostic for PAD. The current studies in normal populations and the correlation with angiography are sparse, and additional trials are needed to further validate the limits. Large-scale trials are needed to establish the risk of morbidity and mortality for the various diagnostic limits of the TBI