What is the initial test for peripheral artery disease?

Initial Diagnostic Test for Peripheral Artery Disease

The resting ankle-brachial index (ABI) is the recommended initial diagnostic test for peripheral artery disease (PAD). 1, 2

Performing the ABI Test

The ABI is a simple, non-invasive test that involves:

• Measuring systolic blood pressures at the arms (brachial arteries) and ankles (dorsalis pedis and posterior tibial arteries) in the supine position using a Doppler device
• Calculating the ABI by dividing the higher of the dorsalis pedis or posterior tibial pressure by the higher of the right or left arm blood pressure 1
• Results should be reported as:
  • Abnormal: ABI ≤0.90
  • Borderline: ABI 0.91-0.99
  • Normal: ABI 1.00-1.40
  • Noncompressible: ABI >1.40 1, 2

Diagnostic Accuracy

The ABI has:

• Sensitivity: 57-79% for detecting arterial stenosis of ≥50% 3
• Specificity: 83-99% for detecting arterial stenosis of ≥50% 4, 3
• Overall accuracy: 72-89% 4

Special Considerations

1. Noncompressible arteries: In patients with ABI >1.40 (often due to medial calcification in diabetes or chronic kidney disease), alternative tests should be used:

   • Toe-brachial index (TBI) (normal >0.70) 1, 2
   • Doppler waveform analysis 1
   • Pulse volume recordings 1

2. Borderline ABI (0.91-0.99) or normal ABI with clinical suspicion:

   • Exercise treadmill ABI testing should be performed 1
   • A post-exercise ABI decrease >20% or ankle systolic blood pressure decrease >30 mmHg is diagnostic for PAD 1

3. Symptomatic patients with normal resting ABI:

   • Exercise treadmill ABI testing increases diagnostic sensitivity 2
   • Consider duplex ultrasound imaging 1

Additional Diagnostic Tests

After confirming PAD with ABI, additional tests may be needed:

1. Segmental leg pressures with pulse volume recordings: Helps localize anatomic segments of disease (aortoiliac, femoropopliteal, infrapopliteal) 1, 2

2. Imaging studies (for patients considering revascularization):

   • Duplex ultrasound: First-line imaging method with 85-90% sensitivity and >95% specificity 1
   • CT angiography: 96-97% sensitivity and 94-98% specificity 1
   • MR angiography: 95% sensitivity and specificity 1

Common Pitfalls

1. Underutilization: Despite being grade 1, level A evidence, ABI is often underutilized in clinical practice. One study found only 22.5% of patients had ABI measured both before and after peripheral vascular intervention 5

2. False negatives: ABI may miss isolated iliac or tibial disease, requiring additional testing in symptomatic patients 2

3. False elevations: Medial calcification in patients with diabetes or chronic kidney disease can lead to falsely elevated ABI values 2

4. Technique variation: Different methods of ABI calculation can affect results. The low ankle pressure (LAP) method has better sensitivity (84% vs 69%) but lower specificity (64% vs 83%) compared to the high ankle pressure (HAP) method 6