What are the recommended diagnostic modalities for peripheral arterial disease (PAD)?

Diagnostic Modalities for Peripheral Arterial Disease

The ankle-brachial index (ABI) is the mandatory first-line diagnostic test for PAD and should be performed in all patients with suspected disease based on history or physical examination findings. 1

Initial Clinical Assessment

Before any diagnostic testing, patients at increased risk require specific evaluation 1:

• Comprehensive symptom review focusing on exertional leg symptoms (claudication), walking impairment, ischemic rest pain, and nonhealing wounds 1
• Vascular examination including palpation of femoral, popliteal, dorsalis pedis, and posterior tibial pulses (rated 0-3: absent, diminished, normal, or bounding) 1
• Auscultation for femoral bruits 1
• Visual inspection of legs and feet for trophic changes 1
• Bilateral arm blood pressure measurement to identify subclavian stenosis (>15-20 mmHg difference is abnormal) and determine the correct arm for ABI calculation 1, 2

Resting Ankle-Brachial Index (ABI)

The resting ABI with or without segmental pressures and waveforms is the Class I recommendation to establish PAD diagnosis 1:

ABI Interpretation 1:

• ≤0.90: Abnormal, confirms PAD
• 0.91-0.99: Borderline, may require exercise testing
• 1.00-1.40: Normal
• >1.40: Noncompressible arteries, requires alternative testing

Technical Performance 1:

• Measure systolic blood pressures at brachial, dorsalis pedis, and posterior tibial arteries using Doppler device in supine position
• Calculate ABI by dividing the higher ankle pressure (dorsalis pedis or posterior tibial) by the higher arm pressure
• Segmental pressures and pulse volume recordings can localize disease to aortoiliac, femoropopliteal, or infrapopliteal segments 1

Alternative Physiological Testing When ABI is Inadequate

Toe-Brachial Index (TBI) 1:

• Class I indication when ABI >1.40 (noncompressible arteries) 1
• Also indicated in patients with diabetes or renal failure where ABI may be falsely elevated 1
• TBI ≤0.70 suggests PAD, though diagnostic thresholds remain less well-established than ABI 3
• Useful for assessing perfusion in suspected critical limb ischemia 1

Exercise Treadmill ABI Testing 1:

• Class I recommendation for patients with exertional non-joint-related leg symptoms and normal or borderline resting ABI (>0.90 and ≤1.40) 1
• Post-exercise ABI decrease >20% serves as diagnostic criterion for PAD 1
• Objectively measures functional limitations attributable to leg symptoms 1
• Can be useful (Class IIa) to assess functional status even in patients with abnormal resting ABI 1

Additional Perfusion Measures for Critical Limb Ischemia 1:

• Transcutaneous oxygen pressure (TcPO₂): <30 mmHg indicates critical limb perfusion 1
• Skin perfusion pressure (SPP): Useful for evaluating local perfusion in nonhealing wounds
• Doppler waveform analysis and pulse volume recordings: Alternative methods when arteries are noncompressible 1

Anatomic Imaging Studies

Anatomic imaging is reserved for symptomatic patients in whom revascularization is being considered—it should NOT be performed in asymptomatic PAD patients 1:

Duplex Ultrasound 1:

• Class I recommendation as first-line imaging method to confirm PAD lesions and anatomic location 1
• Useful to diagnose anatomic location and severity of stenosis for symptomatic patients considering revascularization 1

CTA and MRA 1:

• Class I recommendation for anatomical characterization in symptomatic patients with aortoiliac or multisegmental/complex disease preparing for revascularization 1
• Indicated for guidance of optimal revascularization strategy 1

Invasive Angiography 1:

• Class I recommendation for patients with critical limb ischemia in whom revascularization is considered 1
• Class IIa recommendation for patients with lifestyle-limiting claudication with inadequate response to medical therapy considering revascularization 1
• Class III (Harm): Should NOT be performed for anatomic assessment of asymptomatic PAD 1

Special Populations

Patients with Diabetes or Renal Failure 1:

• Measure toe pressure (TP) or TBI if resting ABI is normal (Class I recommendation)
• Ankle pressures <50 mmHg, toe pressures <30 mmHg, or TcPO₂ <30 mmHg indicate critical limb perfusion 1

Patients with Chronic Wounds 1:

• Consider WIfI (Wound, Ischaemia, and foot Infection) classification system to estimate amputation risk (Class IIa recommendation)
• Use TBI with waveforms, TcPO₂, or SPP to evaluate local perfusion even with normal/borderline ABI 1

Critical Pitfalls to Avoid

• Do not skip ABI measurement: Despite Class I evidence, only 22.5% of patients undergoing intervention had pre- and post-procedure ABI measured in one registry, and those without ABI had worse functional outcomes 4
• Do not rely on ABI alone in diabetes/renal disease: Medial arterial calcification causes falsely elevated ABI; always obtain TBI in these populations 1, 3
• Do not perform anatomic imaging in asymptomatic patients: This is a Class III (Harm) recommendation and exposes patients to unnecessary risk and cost 1
• Do not assume normal ABI excludes PAD in symptomatic patients: Exercise ABI testing is mandatory when resting ABI is normal or borderline with exertional symptoms 1