Peripheral artery disease (PAD) is present in roughly half of people with a diabetes-related foot ulcer, and it is among the strongest predictors of failure to heal and of major amputation. Yet PAD is easy to miss at the bedside in diabetes. Medial arterial calcification stiffens leg arteries and can make standard blood pressure cuff measurements misleadingly normal. This article reviews what current guidelines and systematic reviews say about vascular assessment of the diabetic foot.
Why the Ankle-Brachial Index Alone Is Not Enough
The ankle-brachial index (ABI) compares ankle and arm systolic pressures and is the most familiar vascular screening test. In people with diabetes, however, calcified, non-compressible vessels can falsely elevate ankle pressures, producing a normal or even supranormal ABI despite significant disease. For this reason, the intersocietal guideline from the International Working Group on the Diabetic Foot (IWGDF), the European Society for Vascular Surgery (ESVS) and the Society for Vascular Surgery (SVS) recommends that PAD assessment never rely on a single measurement (Fitridge et al., 2023).
Instead, the guideline advises combining pedal Doppler waveforms with both the ABI and the toe-brachial index (TBI). PAD is considered less likely when the ABI is 0.9–1.3, the TBI is 0.70 or higher, and pedal Doppler waveforms are triphasic or biphasic. Pulse palpation and a thorough history remain part of the examination, and the guideline recommends at least annual clinical assessment for PAD in people with diabetes even when no ulcer is present.
Toe Pressures, TcPO2 and the Prediction of Healing
Digital arteries are far less prone to medial calcification than ankle vessels, which is why toe pressure and the TBI are favoured in diabetes. A companion systematic review of bedside diagnostic tests concluded that no single test is ideal and that combining modalities improves the detection of PAD in this population (Chuter et al., 2024).
Beyond detecting disease, vascular testing helps estimate prognosis. A second systematic review examined how well non-invasive tests predict wound healing or amputation in people with diabetes-related foot ulcers (Chuter et al., 2024). The resulting guideline recommendations are expressed as changes in pre-test probability rather than absolute predictions:
- A toe pressure of 30 mmHg or higher increases the pre-test probability of healing by up to 30%, whereas a value below 30 mmHg increases the probability of major amputation by about 20%.
- A transcutaneous oxygen pressure (TcPO2) of 25 mmHg or higher increases the probability of healing by up to 45%, while a lower value raises the probability of major amputation by about 20%.
- A skin perfusion pressure of 40 mmHg or higher increases the probability of healing by up to 30%.
- An ankle pressure below 50 mmHg or an ABI below 0.5 may be associated with impaired healing.
The guideline rates the certainty of this evidence as low, and these thresholds are best understood as aids to judgment, not rigid cut-offs. A favourable result does not guarantee healing, and a poor result does not make healing impossible.
When Findings Call for Urgent Vascular Referral
The same guideline defines findings consistent with ischaemia as absent pulses, monophasic or absent pedal Doppler waveforms, an ankle pressure below 100 mmHg, or a toe pressure below 60 mmHg (Fitridge et al., 2023). More severe findings, such as an ABI below 0.4, ankle pressure below 50 mmHg, toe pressure below 30 mmHg, TcPO2 below 30 mmHg, or absent pedal waveforms, warrant urgent vascular imaging and consideration of revascularization, particularly in the presence of infection or gangrene.
The guideline also offers a practical safeguard: if an ulcer has not reduced in area by at least 50% after four weeks of optimal standard care, vascular status should be reassessed and specialist input sought, even if earlier tests appeared acceptable. Because the first assessment may have been falsely reassuring, a stalled wound is itself a clinical signal. Before non-emergency foot procedures in people without ulcers, the guideline likewise classifies bedside exclusion of PAD as best practice.
Clinical Summary
Vascular assessment in the diabetic foot is a multi-test process. The ABI is useful but unreliable on its own because of arterial calcification; pedal Doppler waveforms and the toe-brachial index or toe pressure add essential information; and TcPO2 or skin perfusion pressure can substitute when toe pressures cannot be obtained. Toe pressure of 30 mmHg and TcPO2 of 25 mmHg are the most widely cited prognostic thresholds, although the supporting evidence is of low certainty. A wound that fails to improve by half within four weeks should prompt a fresh vascular evaluation. Together, these principles help identify ischaemia early, when revascularization offers the greatest chance of limb salvage.
References
- Fitridge R, Chuter V, Mills J, et al. The intersocietal IWGDF, ESVS, SVS guidelines on peripheral artery disease in people with diabetes and a foot ulcer. Diabetes/Metabolism Research and Reviews (also published in European Journal of Vascular and Endovascular Surgery and Journal of Vascular Surgery). 2023.
- Chuter V, Schaper N, Mills J, et al. Effectiveness of bedside investigations to diagnose peripheral artery disease among people with diabetes mellitus: a systematic review. Diabetes/Metabolism Research and Reviews. 2024.
- Chuter V, Schaper N, Mills J, et al. Performance of non-invasive bedside vascular testing in the prediction of wound healing or amputation among people with foot ulcers in diabetes: a systematic review. Diabetes/Metabolism Research and Reviews. 2024.
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