Does a Toe Wound Require an Ankle-Brachial Index (ABI) Test?
Yes, an ABI should be performed for any toe wound to assess for peripheral artery disease (PAD), as vascular insufficiency is present in up to 50% of diabetic foot ulcers and dramatically increases amputation risk. 1, 2
Initial Vascular Assessment for Toe Wounds
Mandatory Bedside Testing
The ABI is the cornerstone initial diagnostic test for establishing PAD diagnosis in patients with nonhealing wounds, including toe wounds. 1
Formal vascular assessment is mandatory because palpable pulses alone are insufficient—even skilled examiners can miss significant ischemia when pulses are present. 1, 2
Handheld Doppler evaluation should assess flow signals from both dorsalis pedis and posterior tibial arteries to evaluate waveform quality (triphasic waveforms largely exclude PAD). 1, 2
ABI Interpretation for Wound Assessment
The ABI results should guide your next steps: 1
- ABI ≤0.90: Abnormal—confirms PAD
- ABI 0.91-0.99: Borderline—consider additional perfusion testing
- ABI 1.00-1.40: Normal—but still obtain toe pressures if wound is not healing
- ABI >1.40: Noncompressible vessels—ABI is unreliable; proceed directly to toe-brachial index (TBI)
When ABI is Unreliable or Noncompressible
Critical Limitation in Diabetic and Renal Patients
In patients with diabetes or chronic kidney disease, medial arterial calcification causes noncompressible vessels (ABI >1.40), making the ABI falsely elevated and unreliable. 1, 3, 4
Studies show that 43% of symptomatic PAD patients with significant stenosis have normal or inconclusive ABIs (49% in diabetics, 57% in chronic kidney disease patients). 5
Mandatory Alternative Testing
When ABI is >1.40 or unreliable, the TBI with waveforms must be performed to establish PAD diagnosis. 1, 3
TBI ≤0.70 is diagnostic of PAD in patients with noncompressible vessels. 1
TBI has 85% sensitivity and 75% overall accuracy for detecting significant stenosis, compared to only 57% sensitivity for ABI in the general population. 5
Perfusion Thresholds That Predict Wound Healing
When to Obtain Additional Perfusion Measures
If the toe wound is not healing despite optimal care, obtain toe pressure, transcutaneous oxygen pressure (TcPO2), and/or skin perfusion pressure (SPP) to assess healing potential. 1
Specific Thresholds for Clinical Decision-Making
Toe pressure ≥30 mmHg: Increases healing probability by at least 25%; values <30 mmHg warrant urgent vascular imaging and revascularization consideration. 1, 6
TcPO2 ≥25 mmHg: Predicts ulcer healing; values <25 mmHg indicate need for urgent revascularization evaluation. 1, 6, 2
SPP ≥40 mmHg: Associated with increased wound healing likelihood. 1, 2
When to Proceed to Anatomic Imaging
Indications for Urgent Vascular Imaging
Consider urgent duplex ultrasound, CTA, or MRA when: 1, 6, 2
- Toe pressure <30 mmHg
- TcPO2 <25 mmHg
- ABI <0.40 (severe PAD/critical limb ischemia)
- Wound fails to improve within 6 weeks despite optimal management
Revascularization Planning
Invasive angiography is indicated when revascularization is being considered for critical limb ischemia, which these thresholds typically represent. 6
Duplex ultrasound, CTA, or MRA are first-line anatomic imaging options to plan revascularization strategy, with choice depending on institutional availability and patient factors. 1, 6
Common Pitfalls to Avoid
Never assume adequate perfusion based solely on palpable pulses in diabetic patients—objective testing is required. 2
Do not attribute poor wound healing to "diabetic microangiopathy" without excluding macrovascular PAD through proper testing. 1, 2
Do not rely on ABI alone in diabetic patients—the sensitivity drops to 51% in diabetics compared to 66% in non-diabetics due to arterial calcification. 5
When ABI is borderline (0.91-0.99) or mildly reduced (0.70-0.90) with a nonhealing wound, obtain additional perfusion measures (TBI, TcPO2, SPP) to determine if factors other than PAD are contributing. 1