Will the Ankle-Brachial Index (ABI) be low in iliac artery stenosis?

Will ABI Be Low in Iliac Artery Stenosis?

Yes, ABI will typically be low in iliac artery stenosis, but the sensitivity is notably limited—the ABI detects only about 69% of aortoiliac stenoses ≥50%, making it less reliable for proximal disease compared to more distal arterial lesions. 1

Diagnostic Performance for Iliac Artery Disease

The ABI has significantly lower sensitivity for detecting proximal (aortoiliac) stenosis compared to distal disease:

• For aortoiliac stenosis ≥50%: Area under the ROC curve is only 0.69, indicating modest diagnostic accuracy 1
• For aortoiliac occlusion: Slightly better performance with area under curve of 0.83 1
• For comparison, femoral-popliteal disease: Area under curve of 0.77 1
• Overall limb stenosis ≥50%: Much higher area under curve of 0.95 1

This means diagnostic performance is higher for detecting proximal compared with distal lesions is actually incorrect—the data shows the opposite pattern. 1

Why Iliac Stenosis May Not Lower ABI Significantly

Several physiological factors explain the reduced sensitivity:

• Collateral circulation around iliac stenoses can maintain adequate ankle pressures at rest, preventing ABI reduction 1
• Single-level disease in the iliac segment may not create sufficient pressure drop to reduce ABI below 0.90 1
• Resting measurements may appear normal even with hemodynamically significant stenosis 2

Clinical Implications and Pitfalls

The major pitfall is assuming a normal ABI excludes iliac artery stenosis in symptomatic patients. 1

Key considerations:

• Exercise ABI testing dramatically improves sensitivity for proximal disease—in hemodialysis patients, exercise ABI showed 85.7% sensitivity for lesions from iliac to knee, compared to only 42.9% for resting ABI 2
• Duplex ultrasound provides superior accuracy for aortoiliac lesions: 92% sensitivity and 96% specificity 1
• CTA or MRA should be obtained when clinical suspicion remains high despite normal resting ABI 1

Recommended Diagnostic Approach

When iliac artery stenosis is suspected:

1. Measure resting ABI bilaterally as initial screening 1
2. If ABI is normal (>0.90) but symptoms suggest claudication: Perform exercise ABI testing, which causes ankle pressure to decrease more dramatically with proximal stenosis and prolongs recovery time 1, 2
3. If exercise testing is positive or cannot be performed: Proceed directly to duplex ultrasound or cross-sectional imaging (CTA/MRA) 1
4. Do not rely on ABI alone to exclude iliac disease in symptomatic patients—the sensitivity is insufficient 1

Measurement Considerations

• Use Doppler technique rather than oscillometry for better diagnostic performance (area under curve 0.87-0.95 vs 0.80-0.93) 1
• Measure both arms and use the highest brachial pressure as denominator 1, 3
• Calculate ABI for both legs as disease may be asymmetric 1