The Ankle–brachial Index in Peripheral Arterial Disease: A Critical Narrative Review of Diagnostic Performance, Prognostic Value and Contested Screening Roles

Abstract

Peripheral arterial disease is a common manifestation of systemic atherosclerosis that remains frequently unrecognised, partly because most affected people do not report classic intermittent claudication. The ankle–brachial index, the ratio of ankle to arm systolic pressure, has served for more than half a century as the principal non-invasive test for the condition and has acquired a second role as a marker of cardiovascular risk. Its apparent simplicity conceals unresolved questions about measurement standardisation, diagnostic sensitivity in people with diabetes or chronic kidney disease, the meaning of borderline and elevated values, and the value of population screening. This critical narrative review examined how far the evidence supports each of the diagnostic, prognostic, screening and limb-threat roles now assigned to the index. Peer-reviewed literature, clinical practice guidelines and consensus statements were identified through structured searching of international biomedical databases and scholarly indexes, supplemented by citation tracking, and were appraised thematically with attention to study design, reference standards, spectrum of participants and consistency of findings. The synthesis indicates that an index of 0.90 or lower is a highly specific marker of haemodynamically significant disease and a robust, reproducible predictor of cardiovascular events and mortality across diverse cohorts. Sensitivity is modest and deteriorates markedly where medial arterial calcification is common, so that a normal value cannot reliably exclude disease in diabetes, advanced kidney disease or older age. Calculation conventions, device type and operator training materially alter prevalence estimates, and the prognostic signal extends to borderline and non-compressible values, which current diagnostic categories treat inconsistently. Randomised evidence has not shown that screening asymptomatic populations with the index alone improves outcomes, and major guideline bodies therefore diverge. Toe pressures, waveform analysis and data-driven methods may complement the index, but their evidence base is still largely low in certainty. The index remains indispensable as a first-line, context-dependent test, provided that its limitations are acknowledged, its measurement is standardised, and a normal result in high-risk groups is followed by complementary testing. Pragmatic trials of targeted case-finding and diagnostic studies in under-represented populations are the most pressing research needs.