What is the initial diagnostic step for suspected peripheral arterial disease (PAD)?

Diagnostic Testing for Peripheral Arterial Disease

The resting ankle-brachial index (ABI), with or without segmental pressures and waveforms, is the recommended initial diagnostic test for patients with suspected peripheral arterial disease (PAD). 1

Initial Diagnostic Algorithm

Step 1: Resting ABI Measurement

• Performed using a blood pressure cuff and Doppler device to detect blood flow in pedal and brachial arteries
• ABI = ratio of higher systolic pressure in ipsilateral dorsalis pedis and posterior tibial arteries divided by higher of left and right brachial artery systolic pressures
• Interpretation of results:
  • Abnormal: ABI ≤0.90
  • Borderline: ABI 0.91-0.99
  • Normal: ABI 1.00-1.40
  • Noncompressible: ABI >1.40

Step 2: Additional Testing Based on Initial ABI Results

For Normal or Borderline ABI (>0.90 and ≤1.40) with Symptoms:

• Exercise treadmill ABI testing should be performed to evaluate for PAD 1
• This increases diagnostic sensitivity for patients with exertional symptoms but normal resting ABI

For Noncompressible Arteries (ABI >1.40):

• Toe-brachial index (TBI) with waveforms should be performed 1
• Normal TBI: >0.70
• Abnormal TBI: <0.70

For Abnormal ABI (≤0.90):

• Diagnosis of PAD is established
• Exercise treadmill ABI testing can be useful to objectively assess functional status and walking performance 1
• Segmental leg pressures with pulse volume recordings (PVR) and/or Doppler waveforms are reasonable to help delineate the anatomic level of PAD 1

Special Considerations

For Suspected Chronic Limb-Threatening Ischemia (CLTI):

• Additional perfusion assessment is reasonable:
  • Toe pressure/TBI with waveforms
  • Transcutaneous oxygen pressure (TcPO2)
  • Skin perfusion pressure (SPP) 1

For Patients with Nonhealing Wounds or Gangrene:

• Local perfusion measures help determine likelihood of wound healing:
  • Toe pressure/TBI with waveforms
  • TcPO2
  • SPP 1

Common Pitfalls and Limitations

1. Noncompressible Vessels: Particularly common in patients with diabetes and chronic kidney disease due to medial arterial calcification, leading to falsely elevated ABI values (>1.40). Always use TBI when ABI >1.40 1.

2. Normal Resting ABI with Symptoms: Up to 31% of symptomatic patients with normal resting ABI may have abnormal post-exercise ABI, highlighting the importance of exercise testing in symptomatic patients with normal resting values 2.

3. Method of ABI Calculation: The sensitivity of ABI varies based on calculation method. Using the lower of the ankle pressures (LAP method) rather than the higher ankle pressure (HAP method) may increase sensitivity (84% vs 69%) but decrease specificity (64% vs 83%) 3, 4.

4. Operator Dependency: Automated oscillometric methods may be more accurate than manual Doppler measurements when performed by inexperienced operators 5.

5. False Negatives: Isolated iliac or tibial disease may be missed with resting ABI alone, necessitating additional testing in symptomatic patients 6.

The diagnostic approach should follow a systematic algorithm starting with resting ABI and proceeding to additional physiological testing based on clinical presentation and initial ABI results, before considering anatomic imaging studies for patients in whom revascularization is being considered.