What is the role of Ankle-Brachial Index (ABI) testing in diagnosing Peripheral Artery Disease (PAD)?

Role of Ankle-Brachial Index (ABI) Testing in Diagnosing Peripheral Artery Disease

The resting ABI is the first-line and often the only diagnostic test required to establish the diagnosis of PAD in patients with suspected disease, and should be performed in all patients with history or physical examination findings suggestive of PAD. 1

When to Perform ABI Testing

Mandatory Testing (Class I Recommendation)

• Perform ABI in patients with any history or physical examination findings suggestive of PAD, including exertional leg symptoms, claudication, walking impairment, ischemic rest pain, nonhealing wounds, absent pulses, or femoral bruits 1
• Consider ABI screening in asymptomatic patients at increased risk: age ≥65 years, age 50-64 years with atherosclerotic risk factors or family history of PAD, age <50 years with diabetes plus one additional atherosclerotic risk factor, or known atherosclerotic disease in another vascular bed 1

Do Not Perform

• Do not perform ABI in patients without risk factors and without suggestive history or physical examination findings 1

Diagnostic Accuracy

The ABI demonstrates robust diagnostic performance with sensitivity of 68-84% and specificity of 84-99% when using the Doppler method to detect significant stenosis, with areas under the ROC curve of 0.87-0.95 2, 3, 4. While sensitivity can be lower in elderly patients and those with diabetes (as low as 15% in some studies), the high specificity (83.3-99.0%) and accuracy (72.1-89.2%) make it an excellent rule-in test for PAD 5, 4.

Proper ABI Measurement Technique

Critical Technical Requirements

• Patient must be supine for at least 5 minutes before measurement 6
• Measure in this exact sequence: first arm systolic blood pressure, first posterior tibial artery, first dorsalis pedis artery, other posterior tibial artery, other dorsalis pedis artery, then other arm 6
• If the first arm exceeds the other arm by >10 mmHg, repeat the first arm measurement and discard the initial reading 6
• Calculate ABI by dividing the highest ankle pressure (either posterior tibial or dorsalis pedis) by the highest brachial pressure 6, 3

Common Measurement Pitfalls to Avoid

• Using only one ankle artery or the higher ABI between legs will miss significant disease—always use the lower ABI of both legs to identify more individuals at cardiovascular risk 6
• Failure to rest the patient adequately will produce inaccurate results 6
• Proper training is essential—measurements should be performed by qualified individuals with both didactic and experiential training in vascular anatomy, physiology, and Doppler device function 6

Interpreting ABI Results

Standardized Reporting Categories

• ABI ≤0.90: Abnormal—confirms PAD diagnosis 1, 2
• ABI 0.91-0.99: Borderline—warrants further evaluation for cardiovascular risk 1, 6
• ABI 1.00-1.40: Normal range 1, 6
• ABI >1.40: Noncompressible vessels—requires alternative testing 1, 6

Clinical Significance

An ABI <0.90 is a powerful independent marker of cardiovascular risk, with inverse correlation to non-fatal cardiac events (myocardial infarction, stroke, heart failure) and mortality 7. Patients with PAD have 2.99 times higher risk of all-cause mortality and 2.35 times higher risk of cardiovascular mortality compared to those without PAD 8.

When Resting ABI is Insufficient

For Noncompressible Vessels (ABI >1.40)

Measure toe-brachial index (TBI) in patients with ABI >1.40, which commonly occurs with diabetes or advanced chronic kidney disease—a TBI ≤0.70 is diagnostic of PAD 1, 2, 3

For Normal or Borderline ABI with Symptoms

Perform exercise treadmill ABI testing in patients with exertional non-joint-related leg symptoms and normal or borderline resting ABI (0.90-1.40)—a post-exercise ankle pressure decrease >30 mmHg or ABI decrease >20% confirms PAD 1, 3

For Anatomic Localization

Segmental lower extremity blood pressures with pulse volume recordings and/or Doppler waveforms can localize anatomic disease segments (aortoiliac, femoropopliteal, infrapopliteal) and are particularly useful when planning revascularization 1, 3

Role of Advanced Imaging

Anatomic imaging studies (duplex ultrasound, CTA, MRA, invasive angiography) are not required for initial PAD diagnosis but are reserved for symptomatic patients being considered for revascularization 1, 3. Duplex ultrasound serves as the first-line imaging method to confirm PAD lesions and guide revascularization strategy after ABI screening 1, 2.

Key Clinical Caveat

Physical examination findings alone are insufficient—objective testing with ABI is mandatory to confirm the diagnosis 3. However, for practical clinical diagnosis, an ABI of 0.80 is sufficient to confirm PAD considering the 95% confidence interval of measurement differences is 0.10 6. When ABI values are close to the 0.90 threshold, reproducibility becomes crucial, and repeat measurements may be warranted 6.