What is the initial diagnostic test for patients suspected of having peripheral artery disease (PAD), Ankle-Brachial Index (ABI) or arterial Doppler?

Ankle-Brachial Index (ABI) is the Initial Diagnostic Test for Suspected Peripheral Artery Disease

The ankle-brachial index (ABI) is recommended as the first-line non-invasive test for the diagnosis of peripheral artery disease (PAD) in patients with suspected disease. 1

Rationale for ABI as Initial Test

• ABI is a low-cost, easy-to-use diagnostic tool with high specificity (83-99%) for detecting significant arterial stenosis 2, 3
• The 2024 ACC/AHA guidelines explicitly state that in patients with suspected PAD, the resting ABI with or without pulse volume recordings (PVR) and/or Doppler waveforms is recommended to establish the diagnosis 1
• ABI provides objective measurement that helps stratify cardiovascular risk beyond standard risk scores 1

ABI Measurement and Interpretation

• ABI results are categorized as:

  • Normal: 1.00-1.40
  • Borderline: 0.91-0.99
  • Abnormal (diagnostic of PAD): ≤0.90
  • Noncompressible vessels: >1.40 1, 4

• When performing ABI:

  • Use the lower of the ankle pressures (posterior tibial or dorsalis pedis) for each leg 1
  • Use the higher of the two brachial pressures 1
  • The lower ABI of the two legs should be used for diagnosis and risk assessment 1

Diagnostic Algorithm for Suspected PAD

1. Initial test: Resting ABI with or without PVR/Doppler waveforms 1

2. If ABI ≤0.90: PAD diagnosis confirmed 1

   • Consider segmental leg pressures with PVR/Doppler waveforms to help delineate anatomic level of PAD 1

3. If ABI is borderline (0.91-0.99) or normal (1.00-1.40) but clinical suspicion remains:

   • Perform exercise treadmill ABI testing 1
   • A post-exercise ankle pressure decrease >30 mmHg or ABI decrease >20% confirms PAD 1

4. If ABI >1.40 (noncompressible vessels):

   • Perform toe pressure/toe-brachial index (TBI) with waveforms 1
   • TBI ≤0.70 is considered abnormal 1
   • Consider transcutaneous oxygen pressure (TcPO₂) or skin perfusion pressure (SPP) measurements 1

5. For patients with suspected chronic limb-threatening ischemia (CLTI):

   • Use toe pressure/TBI with waveforms, TcPO₂, and/or SPP in addition to ABI 1

When to Consider Arterial Doppler Ultrasound

Arterial Doppler ultrasound is not the initial diagnostic test but should be used:

• After ABI confirms PAD diagnosis, to assess arterial anatomy and hemodynamics before revascularization 1
• When ABI results are inconclusive or technically inadequate 1
• To locate and quantify stenotic lesions 4
• For post-revascularization surveillance 1

Limitations and Considerations

• ABI has lower sensitivity (65-79%) than specificity, particularly in elderly patients and those with diabetes 2, 5, 3
• Medial arterial calcification in diabetes and chronic kidney disease can falsely elevate ABI values 1, 5
• Semi-automatic oscillometric devices may provide comparable diagnostic accuracy to Doppler-based measurements with shorter measurement time 6

Clinical Implications

• An abnormal ABI (≤0.90) identifies patients at increased risk of cardiovascular events and mortality 1, 4
• Early diagnosis with ABI allows for timely implementation of guideline-directed medical therapy and risk factor modification 4
• Regular ABI monitoring helps assess disease progression and treatment effectiveness 4

The diagnostic approach to PAD should follow a logical sequence starting with ABI as the cornerstone test, with additional testing based on initial results and clinical presentation.