Diagnosis guide
Circulation tests for foot wounds: ABI, toe pressures and TcPO2
How ankle and toe pressures, Doppler waveforms, TcPO2 and artery imaging measure blood flow to a foot wound, and how the results guide healing, surgery and vascular referral.
Medically reviewed by Dr. Efe Ozturk · Last reviewed
Why every foot wound needs a circulation check
With diabetes, the usual warnings of poor circulation can be missing: nerve damage can hide the pain of blocked arteries and leave the foot feeling warm.[1]
Feeling for pulses is the first step, but on its own it can’t reliably rule PAD out.[1,4] The international diabetic foot guideline recommends three bedside tests together for anyone with diabetes and a foot ulcer or gangrene: Doppler waveforms from the foot arteries, the ankle-brachial index (ABI) and the toe-brachial index (TBI). The same tests are advised before foot surgery with diabetes, except emergency surgery for severe infection.[1]
At our practice we check your pulses and do noninvasive circulation testing. For warning signs, see poor circulation in the feet (external site) from our parent practice and our Nerve Institute’s guide to cold or numb feet (external site).
The ankle-brachial index test
The ABI is usually the first test for PAD. A blood pressure cuff and a Doppler device that picks up blood flow measure the pressure at your ankle and in your arm, and the ABI is the ratio of the two.[3,2] Two ankle arteries are checked, the dorsalis pedis and the posterior tibial.[2] You lie flat, and exercise or caffeine just beforehand can throw the numbers off.[1]
Swipe sideways to see the whole drawing.
US guidelines sort results into four bands:[2]
- 0.90 or lower: abnormal
- 0.91–0.99: borderline
- 1.00–1.40: normal
- Above 1.40: “noncompressible”: the ankle arteries are too stiff for the cuff to squeeze, so the number can’t be trusted
An ABI under 0.40 is a sign of severe PAD.[3]
When the ABI looks normal but blood flow isn’t
With diabetes, calcium often builds up in the walls of the leg arteries (medial arterial calcification), raising ankle readings and, less so, toe readings.[1] Stiff arteries below the knee are common with diabetes or chronic kidney disease and can push the ABI above 1.40 even when imaging shows significant blockages.[2]
A reading in the normal range can mislead too. Nearly one in four people with chronic limb-threatening ischemia, the stage of PAD that puts the foot at risk, has an ABI between 0.90 and 1.40. In this group, only 58% of people with abnormal toe pressures also have an abnormal ABI.[2] With kidney disease, see foot wounds with kidney disease.
Toe pressures and the toe-brachial index
The small arteries of the toes rarely become too stiff to compress, so a toe pressure is the next step when the ABI can’t be trusted.[2] The test measures the blood pressure in your big toe; divided by the arm pressure, it gives the TBI, and a TBI under 0.70 suggests PAD.[3,2,1]
Toe pressures reflect blood flow to the forefoot and toes, where most diabetic foot ulcers form. In the guideline’s review, a toe pressure of 30 mmHg or more raised the likelihood of healing by up to 30%, and a lower reading the likelihood of a major amputation by about 20%.[1]
A handheld Doppler probe also records the shape of each pulse signal (the waveform). Two or three phases (biphasic or triphasic) make PAD less likely, while a single-phase (monophasic) or absent signal is a sign of severe ischemia.[1]
TcPO2 and skin perfusion pressure
Transcutaneous oxygen pressure (TcPO2) measures oxygen in the skin beside a wound, not inside it.[5] Measured at the tissue level, it reflects both large arteries and the smallest vessels.[1] A low reading doesn’t always mean blocked arteries, since a barrier that slows oxygen moving through the tissue can also lower it.[5]
In the guideline’s review, a TcPO2 of 25 mmHg or more raised the likelihood of healing by up to 45%, and a lower value the likelihood of a major amputation by about 20%.[1] In one lower-quality study, a skin perfusion pressure of 40 mmHg or more raised the likelihood of healing by up to 30%.[1] Both are second-line tests because the equipment is costlier and harder to find; they help most when toe pressures can’t be measured, such as after a forefoot amputation.[1]
Imaging that maps the arteries
When a procedure to restore blood flow is considered, imaging maps the arteries from the aorta to the foot, with detailed views below the knee.[1] The choice depends on your health, including kidney function, and on local equipment and expertise.[1,2,3]
| Test | How it’s done | Things to know |
|---|---|---|
| Arterial duplex ultrasound | A handheld probe shows the arteries and how fast blood flows | Uses sound waves; depends on the technologist’s skill; calcium can limit the view |
| CT angiography | Dye is injected and X-rays are taken | Detailed; uses dye and radiation; calcium can limit the view |
| MR angiography | A magnetic scanner images the arteries, with or without dye | No X-rays; some dyes are avoided in severe kidney disease; may not be safe with metal implants |
| Catheter angiography | A thin tube is passed into a groin artery, then dye is injected and X-rays taken | The reference standard below the knee; radiation, dye and a risk of bleeding at the entry site |
With advanced kidney disease, a catheter angiogram may need less dye than a CT scan, and when a procedure is planned it can map the arteries and open a blockage in one session.[2] We arrange arterial duplex ultrasound and angiography with vascular specialists.
How the results shape treatment and surgery
The results help judge whether a foot operation is likely to heal, and they steer the plan:[1]
- Enough blood flow. We can move ahead with the surgery the wound needs, from draining infection and removing infected bone to correcting the deformity behind the ulcer (see limb salvage surgery).
- Signs of ischemia. Absent pulses, an ankle pressure under 100 mmHg or a toe pressure under 60 mmHg mean a vascular specialist should be consulted.[1] The referral is urgent with severe ischemia: an ABI under 0.4, an ankle pressure under 50 mmHg, a toe pressure or TcPO2 under 30 mmHg, or single-phase or absent waveforms.[1] We make the referral and time your surgery with the vascular team (see restoring blood flow).
- Infection with poor circulation. Infection or gangrene with PAD calls for an urgent vascular consultation to time drainage and the blood-flow procedure.[1]
- After blood flow is restored. Perfusion is rechecked, because treated arteries can narrow again.[1] A TcPO2 under 40 mmHg is linked with poorer healing after an amputation.[5] When a partial foot amputation is needed, the readings help plan one that heals and keeps as much of the foot as possible.
- A wound that stalls. If it hasn’t shrunk by half in 4 weeks despite good wound care, offloading and control of infection and blood sugar, blood flow is rechecked and a vascular specialist consulted.[1]
- Normal results, slow healing. Good numbers turn the search to other causes before anyone blames “small vessel disease.”[1,2]
No single number decides: infection, the size and depth of the wound and pressure on it also affect healing.[1] Dr. Efe Ozturk, a Foot and Ankle Surgeon who is board certified in wound care (FAPWH), reads the results alongside the wound. These readings also inform a second opinion before amputation.
Limits and risks
The bedside tests are noninvasive and simple, with minimal risk.[2,1] Their limit is accuracy: the healing thresholds come from small, lower-quality studies with differing cutoffs, and no single test has been shown to be ideal, so several are combined.[1] Imaging carries more risk, since CT and catheter angiography use radiation and dye.[2]
Toe pressures and TcPO2 are measured in a warm room, because cold makes arteries tighten.[2] Wear clothes that let you uncover your lower legs, and bring earlier vascular test results.
When to seek care
See us within a day or two for any foot wound that isn’t healing, especially if you have diabetes. With diabetes or poor circulation, call us the same day for signs of infection (see a red, hot, swollen foot) or new foot pain at rest (see foot pain at night). For a toe changing color, see dark or black toes.
References
- 1.Fitridge R, Chuter V, Mills J, Hinchliffe R, Azuma N, Behrendt CA, et al. The intersocietal IWGDF, ESVS, SVS guidelines on peripheral artery disease in people with diabetes and a foot ulcer. Diabetes Metab Res Rev. 2024;40(3):e3686. PubMed 37726988 (external site)
- 2.Gornik HL, Aronow HD, Goodney PP, Arya S, Brewster LP, Byrd L, et al. 2024 ACC/AHA/AACVPR/APMA/ABC/SCAI/SVM/SVN/SVS/SIR/VESS Guideline for the Management of Lower Extremity Peripheral Artery Disease: A Report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. Circulation. 2024;149(24):e1313-e1410. PubMed 38743805 (external site)
- 3.National Heart, Lung, and Blood Institute. Peripheral Artery Disease: Diagnosis. NIH. nhlbi.nih.gov (external site)
- 4.Forsythe RO, Apelqvist J, Boyko EJ, et al. Effectiveness of bedside investigations to diagnose peripheral artery disease among people with diabetes mellitus: A systematic review. Diabetes Metab Res Rev. 2020;36 Suppl 1:e3277. PubMed 32176448 (external site)
- 5.Fife CE, Smart DR, Sheffield PJ, et al. Transcutaneous oximetry in clinical practice: consensus statements from an expert panel based on evidence. Undersea Hyperb Med. 2009;36(1):43-53. PubMed 19341127 (external site)
This page is general health information and isn’t a substitute for advice from a clinician who knows your history. Read our medical disclaimer and how we review content.
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Narrowed leg arteries that starve a foot wound of blood, and the vascular procedures and foot surgery that aim to restore circulation, heal the wound and keep the foot.
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Angioplasty, stents and bypass, performed by vascular specialists, restore blood flow to a foot wound that is starved of it; we test circulation, refer you and time foot surgery and wound care around the procedure.
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Foot ulcers and wounds in people with advanced kidney disease or on dialysis, who face a higher risk and need circulation testing and wound care, with any surgery planned alongside their kidney care.
Diagnosis guide
How wounds are evaluated
How a foot wound is evaluated, from the exam and measurements to the probe-to-bone test, cultures, X-rays, MRI, bone biopsy and circulation checks.