Ankle-Brachial Index (ABI)

What is the ABI (Cheville-Bras index)?

The ankle-brachial index (ABI) is the ratio of ankle systolic blood pressure to brachial systolic blood pressure.

It is a simple, non-invasive test commonly used to detect or suggest peripheral artery disease (PAD) and to support cardiovascular risk assessment.

How is it calculated (standard method)?

• Measure systolic pressures in both arms (brachial).
• Use the higher brachial systolic pressure as the denominator for both legs.
• For each leg, use the higher ankle pressure (dorsalis pedis or posterior tibial) as the numerator.
• Compute ABI separately for each leg; the lower ABI is often used to summarize the “worst leg”.

Interpretation

• ABI ≤ 0.90: Abnormal — consistent with PAD.
• ABI 0.91–0.99: Borderline.
• ABI 1.00–1.40: Normal.
• ABI > 1.40: Noncompressible arteries (stiff/calcified) — consider TBI.
• If ABI is normal/borderline but symptoms persist, exercise ABI can improve sensitivity.

How to use the result

This tool supports clinical judgment and should be interpreted within local protocols and the patient context. ABI is a screening/assessment test, not a standalone diagnosis.

• Ensure pressures are measured at rest using appropriate cuff size and Doppler technique when available.
• Use the higher brachial pressure to avoid underestimating PAD when there is subclavian stenosis.
• ABI > 1.40 can occur with arterial calcification (e.g., diabetes/CKD/older age): consider TBI.
• In symptomatic patients with normal/borderline ABI, consider exercise ABI and clinician evaluation.