What is the preferred initial test for diagnosing peripheral artery disease (PAD), Ankle-Brachial Index (ABI) or duplex testing?

Ankle-Brachial Index (ABI) is the Preferred Initial Test for Diagnosing Peripheral Artery Disease

The resting ankle-brachial index (ABI), with or without segmental pressures and waveforms, is recommended as the first-line diagnostic test for peripheral artery disease (PAD) in patients with suspected disease. 1, 2

Diagnostic Algorithm for PAD

Initial Assessment

• For patients with suspected PAD (history of claudication, ischemic rest pain, nonhealing wounds, or risk factors), begin with:
  • Resting ABI measurement using Doppler technique (higher accuracy than oscillometric or palpation methods) 2
  • ABI calculation: Highest ankle systolic pressure / Highest brachial systolic pressure 2

ABI Interpretation

• ABI results should be categorized as 1, 2:
  • Abnormal: ≤0.90 (confirms PAD diagnosis)
  • Borderline: 0.91-0.99 (requires additional testing)
  • Normal: 1.00-1.40
  • Noncompressible vessels: >1.40 (requires alternative testing)

Follow-up Testing Based on ABI Results

1. If ABI ≤0.90: PAD diagnosis confirmed

   • Proceed with risk assessment and treatment planning
   • Consider duplex ultrasound for anatomical characterization if revascularization is being considered 1

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

   • Perform exercise treadmill ABI testing 1, 3
   • Exercise testing can identify PAD in 31% of symptomatic patients with normal resting ABI 3

3. If ABI >1.40 (noncompressible vessels):

   • Perform toe-brachial index (TBI) measurement 1, 2
   • Consider pulse volume recordings or Doppler waveform analysis 1, 2
   • Note: Noncompressible vessels are common in diabetes and chronic kidney disease 2

4. For anatomical assessment when revascularization is considered:

   • Duplex ultrasound is indicated as first-line imaging method 1
   • CT angiography (CTA) or MR angiography (MRA) may also be used 1

Evidence Quality and Considerations

Strengths of ABI Testing

• ABI is simple, noninvasive, and inexpensive 1, 2
• High specificity (83.3-99.0%) for detecting significant stenosis 4
• Provides prognostic information: abnormal ABI (≤0.90) identifies patients with approximately twice the risk of myocardial infarction and cardiovascular death 2

Limitations of ABI Testing

• Variable sensitivity (15-79%) for PAD diagnosis, particularly in elderly and diabetic patients 4
• Limited utility in patients with calcified vessels 3
• May miss PAD in symptomatic patients with normal resting ABI 3

Role of Duplex Ultrasound

• Duplex ultrasound provides detailed anatomical information about location and severity of stenosis 1, 2
• Indicated for anatomical characterization when revascularization is considered 1
• Not recommended as the initial diagnostic test for PAD 1

Common Pitfalls and Caveats

• Relying solely on resting ABI in symptomatic patients with normal results may miss PAD; consider exercise ABI testing 3
• Noncompressible vessels (ABI >1.40) correlate with higher cardiovascular mortality and should not be dismissed as normal 5
• ABI should be measured in both arms to identify the higher systolic pressure for accurate calculation 1
• Failure to perform ABI before peripheral vascular interventions may lead to decreased functional status after intervention 6

In conclusion, while both ABI and duplex ultrasound are valuable tools in PAD assessment, the evidence clearly supports using ABI as the initial diagnostic test, with duplex ultrasound reserved for anatomical characterization when revascularization is being considered.