Validation of a Standardised Duplex Ultrasound Classification System for the Reporting and Grading of Peripheral Arterial Disease

Introduction
Duplex ultrasound (DUS), a non-invasive means of arterial mapping, allows for reliable diagnosis of peripheral arterial disease (PAD). One of our authors (CPO), developed a standardised DUS-based scoring system, devised for rapid detection and reporting of PAD. The purpose of this study is to validate this system, determining diagnostic performance both overall, and per disease severity.

Methods
250 participants were recruited, based on diagnosis (N = 125), or absence of PAD (N = 125) from GP registers. Right and left legs per subject were handled as independent readings, determining actual PAD status via ABPI <0.9, and then further grading disease severity using suggested ABPI ranges. Data were excluded if no corresponding ABPI value was obtained per DUS-determination, or if the ABPI reading was >1.4, owing to risk of false negatives due to incompressible vessels. Diagnostic sensitivity and specificity were obtained overall, and per severity classification. Furthermore, interrater agreement between ABPI- and DUS-determined PAD severity was determined by linear weighted Cohen’s Kappa.

Results
The sensitivity and specificity in the detection of disease overall was 81.0% (95% CI 73.4 - 87.2%) and 86.3% (95% CI 82.3 – 89.8%), respectively. From mild to severe PAD, sensitivity increased from 71.1% (95% CI 55.7 – 83.6%) to 89.3% (95% CI 71.8 – 97.7%). Furthermore, a Cohen Kappa value of 0.63 (95% CI 0.57 – 0.69) was obtained, indicating moderate agreement between the two diagnostic methods.

Conclusions
Findings in this study validate the diagnostic performance of the standardised DUS scoring system, as well as its capacity to grade severity of disease, offering a potential tool for the identification of PAD in the community / research settings following initial screening methods. Confirmatory work could include a comparison of DUS-determined disease with gold-standard methods of non-invasive angiography, and novel tools such as toe-flex NIRS and multi-site photoplethysmography.