Perform Resting ABI Immediately
In a patient with symptoms of PAD or CLTI who has not had an ABI test, the next best step is to obtain a resting ankle-brachial index (ABI) with or without pulse volume recordings (PVR) and/or Doppler waveforms to establish the diagnosis. 1
Diagnostic Algorithm Based on ABI Results
If ABI ≤0.90 (Abnormal - PAD Confirmed)
- Initiate guideline-directed medical therapy immediately including antiplatelet therapy, statin therapy, and blood pressure control 1, 2
- For CLTI presentation (rest pain, nonhealing wounds, or gangrene): Obtain additional perfusion measures including toe-brachial index (TBI) with waveforms, transcutaneous oxygen pressure (TcPO2), and/or skin perfusion pressure (SPP) to assess tissue viability and predict wound healing 1, 2
- Proceed to anatomic imaging (duplex ultrasound, CTA, or MRA) if symptoms are functionally limiting or revascularization is being considered 1, 3
- If ABI <0.4, this indicates severe PAD with critical limb ischemia requiring urgent vascular consultation and revascularization planning 3
If ABI 0.91-0.99 (Borderline)
- Perform exercise treadmill ABI testing if the patient has exertional non-joint-related leg symptoms to unmask PAD 1
- Nearly 31% of symptomatic patients with normal resting ABI will have abnormal post-exercise ABI, confirming PAD 4
- If CLTI is suspected despite borderline ABI (nonhealing wounds or gangrene), obtain TBI with waveforms, TcPO2, or SPP as the ABI may be falsely reassuring 1
If ABI 1.00-1.40 (Normal Range)
- Do not stop here if symptoms persist - approximately 46% of symptomatic patients referred for PAD evaluation have normal resting ABI 4
- Perform exercise treadmill ABI testing for patients with exertional leg symptoms to differentiate claudication from pseudoclaudication 1
- For CLTI presentation with normal ABI, obtain TBI with waveforms, TcPO2, or SPP as toe pressures may be discordant with ankle pressures, particularly in diabetes 1
If ABI >1.40 (Noncompressible Vessels)
- The ABI is unreliable - this indicates medial arterial calcification, common in diabetes mellitus and chronic kidney disease 1, 5
- Immediately obtain TBI with waveforms as the primary alternative test - digital arteries are rarely noncompressible 1, 5
- A TBI ≤0.70 confirms PAD diagnosis 1, 5, 2
- Consider adding Doppler waveform analysis or pulse volume recordings, which rely on limb volume change rather than pressure 5
Critical Pitfalls to Avoid
Do not rely solely on resting ABI in symptomatic patients - research demonstrates that 46% of symptomatic patients have normal resting ABI, and 31% of these will have abnormal post-exercise ABI 4. The sensitivity of resting ABI alone is insufficient for ruling out PAD in symptomatic individuals 4, 6.
Do not skip TBI in diabetic patients - even with normal ABI values (0.90-1.40), diabetic patients with nonhealing wounds may have significant PAD detectable only by TBI, as arterial calcification can falsely elevate ankle pressures 1, 6.
Recognize that classic claudication is uncommon - only 11% of PAD patients present with classic claudication symptoms, while 50% have atypical leg symptoms and 40% are asymptomatic 7, 8. Therefore, maintain high clinical suspicion even with atypical presentations.
Physician awareness of PAD is poor - studies show only 49% of physicians were aware of PAD diagnosis even when documented in medical records, and 55% of PAD cases were newly diagnosed during systematic screening 8. This underdiagnosis leads to inadequate secondary prevention, with PAD patients receiving less intensive treatment than those with coronary artery disease 8.
Additional Perfusion Measures for CLTI
When CLTI is suspected (rest pain, nonhealing wounds, gangrene), obtain these additional tests regardless of ABI value 1, 2: