Peripheral artery disease (PAD) is present in roughly half of people with diabetes-related foot ulcers, and it is one of the strongest determinants of whether an ulcer heals or leads to amputation. Yet the bedside tests used to detect it are not equally reliable in diabetes. Understanding what each perfusion measurement can and cannot tell a clinician is central to timely vascular referral and limb preservation.
Why the Ankle-Brachial Index Falls Short in Diabetes
The ankle-brachial index (ABI) compares ankle and arm systolic pressures. In people with diabetes or chronic kidney disease, medial arterial calcification stiffens the tibial vessels so they resist cuff compression, producing falsely normal or even elevated readings. A 2022 systematic review by Brouwers and colleagues in eClinicalMedicine examined 23 diagnostic studies in patients prone to medial calcification. An ABI below 0.9 was useful for confirming PAD (positive likelihood ratios of roughly 8.7 to 17 in studies that excluded values above 1.3), but it frequently failed to exclude disease: in 16 of 18 ABI studies the negative likelihood ratio exceeded 0.2. Including patients with an ABI above 1.3 reduced accuracy further. The authors cautioned against relying on any single bedside test in this population.
Toe Pressure, Toe-Brachial Index, and Transcutaneous Oxygen
Digital arteries are far less prone to calcification, which is why toe-based measures are preferred. The IWGDF guideline on PAD (Hinchliffe et al., 2020) and the later intersocietal guideline (Fitridge et al., 2023) recommend that the ABI be interpreted alongside at least one additional test, such as toe pressure with toe-brachial index (TBI), transcutaneous oxygen pressure (TcPO2), or skin perfusion pressure. A TBI of 0.75 or higher makes significant PAD unlikely, whereas a toe pressure below 30 mmHg or a TcPO2 below 25 mmHg should prompt urgent vascular imaging and consideration of revascularisation.
The toe-based tests have limits too. In the Brouwers review, no TBI study showed a large effect for ruling in PAD, with positive likelihood ratios between 1.6 and 4.3, and five of six studies could not reliably rule it out. Continuous-wave Doppler waveform analysis, where preservation of a triphasic pattern argues against PAD, performed best for exclusion, although only two studies evaluated it. These findings explain why guidelines advise combining a clinical pulse examination, Doppler waveforms, and a pressure-based measurement rather than depending on one number.
Predicting Healing and Amputation
Forsythe and colleagues (2020), in a systematic review for the IWGDF, assessed how well perfusion markers predict wound healing or major amputation in diabetic foot ulcers. A toe pressure of at least 30 mmHg gave positive likelihood ratios for healing between about 1.1 and 5.0, while TcPO2 of at least 25 mmHg and skin perfusion pressure of at least 40 mmHg were generally stronger, with some studies reporting ratios above 5. ABI performed weakly for predicting healing, with most ratios between 1.0 and 3.1, and a normal ABI was not useful for this purpose. For major amputation, an ankle pressure below 50 mmHg or ABI below 0.5 carried the strongest single result (positive likelihood ratio 8.2). The authors rated the evidence as moderate in quality and inconsistent, with many of the most striking results arising from small single-centre studies.
The IWGDF guidance therefore treats these thresholds as modifiers of pre-test probability, not absolute cut-offs. Values such as toe pressure of at least 30 mmHg, TcPO2 of at least 25 mmHg, or skin perfusion pressure of at least 40 mmHg raise the likelihood of healing by at least 25 percentage points, but they do not guarantee it.
Perfusion Testing Within the Wider Clinical Picture
Because no test is definitive, guidelines add a clinical trigger: if a foot ulcer has not improved within about six weeks despite optimal standard care, vascular imaging and revascularisation should be considered irrespective of bedside results. Perfusion testing should also be repeated when healing stalls, since disease can progress, and it should be interpreted together with infection, neuropathy, and offloading, all of which influence outcomes independently. The 2023 intersocietal guideline further emphasises that any person with diabetes, a foot ulcer, and suspected PAD should be assessed by a multidisciplinary team with vascular expertise.
Key Takeaways
Calcified vessels make the ankle-brachial index unreliable in diabetes, so a normal value does not exclude PAD. Toe pressure, toe-brachial index, TcPO2, skin perfusion pressure, and Doppler waveforms offer complementary information, and each has recognised limitations. Predictive accuracy for healing and amputation is moderate at best, which is why test results are best viewed as probabilities integrated with the clinical course, including failure to improve over six weeks.
References
- Brouwers JJWM, Willems SA, Goncalves LN, Hamming JF, Schepers A. Reliability of bedside tests for diagnosing peripheral arterial disease in patients prone to medial arterial calcification: a systematic review. eClinicalMedicine. 2022;50:101532.
- Forsythe RO, Apelqvist J, Boyko EJ, et al. Performance of prognostic markers in the prediction of wound healing or amputation among patients with foot ulcers in diabetes: a systematic review. Diabetes/Metabolism Research and Reviews. 2020;36(S1):e3278.
- Hinchliffe RJ, Forsythe RO, Apelqvist J, et al. Guidelines on diagnosis, prognosis, and management of peripheral artery disease in patients with foot ulcers and diabetes (IWGDF 2019 update). Diabetes/Metabolism Research and Reviews. 2020;36(S1):e3276.
- 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, European Journal of Vascular and Endovascular Surgery, and Journal of Vascular Surgery. 2023.
Comments
