mmHg
Highest of dorsalis pedis or posterior tibial artery reading
Enter ankle systolic pressuremmHg
Highest reading from either arm
Enter brachial systolic pressureAnkle-Brachial Index (ABI)
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⚕️ Clinical Disclaimer: This calculator is for educational purposes only. ABI results must be interpreted by a qualified healthcare provider in conjunction with clinical history, symptoms, and physical examination. Do not use this tool to self-diagnose or alter treatment without medical guidance.
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What Is the Ankle-Brachial Index (ABI)?
The Ankle-Brachial Index (ABI) is a simple, non-invasive diagnostic test used to screen for peripheral artery disease (PAD) — arterial blockages in the legs caused by atherosclerosis. It compares blood pressure at the ankle to blood pressure at the arm (brachial artery). A lower ankle pressure relative to arm pressure indicates reduced blood flow, which is a marker of arterial narrowing.
ABI Formula
ABI = Ankle Systolic Pressure ÷ Brachial (Arm) Systolic Pressure
Use the highest ankle reading (dorsalis pedis or posterior tibial) and the highest arm reading (left or right brachial)
Example: 132 mmHg ankle ÷ 140 mmHg arm = ABI 0.94 (Normal)
Example: 132 mmHg ankle ÷ 140 mmHg arm = ABI 0.94 (Normal)
ABI Interpretation Ranges
- >1.40 — Non-compressible vessels: Falsely elevated, often in diabetes or chronic kidney disease. Requires toe-brachial index (TBI) or duplex ultrasound.
- 1.00–1.40 — Normal: No significant PAD. Ankle pressure equals or exceeds arm pressure.
- 0.91–0.99 — Borderline: Possible mild PAD. Monitor, manage risk factors, repeat in 1 year.
- 0.71–0.90 — Mild PAD: Claudication often present. Exercise therapy, risk factor modification, antiplatelet therapy.
- 0.41–0.70 — Moderate PAD: Significant ischemia. Likely claudication at short distances. Vascular specialist referral.
- ≤0.40 — Severe/Critical Limb Ischemia: Rest pain, tissue loss risk. Urgent vascular surgery evaluation needed.
💡 PAD Prevalence: Peripheral artery disease affects approximately 8–12 million Americans. Risk factors include smoking (strongest modifiable risk), diabetes, hypertension, hyperlipidemia, age over 65, and chronic kidney disease. ABI screening is recommended for all adults over 65 and for adults over 50 with diabetes or smoking history.
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Frequently Asked Questions
What is a normal ABI value?
A normal ABI is 1.00–1.40. This means ankle blood pressure equals or slightly exceeds arm blood pressure, indicating unobstructed arterial flow to the lower extremities. An ABI of 0.91–0.99 is considered borderline and warrants monitoring. Values below 0.90 are diagnostic for peripheral artery disease (PAD). Values above 1.40 indicate non-compressible, calcified vessels (common in diabetes) and require alternative testing.
What does a low ABI indicate?
A low ABI (below 0.90) indicates peripheral artery disease (PAD) — arterial blockages in the legs due to atherosclerosis. Severity: Mild PAD (0.71–0.90) causes intermittent claudication (leg cramps during walking). Moderate PAD (0.41–0.70) causes claudication at short distances and may cause rest pain. Severe/critical limb ischemia (≤0.40) involves rest pain, tissue breakdown, and risk of amputation. PAD is also a strong marker for coronary artery disease.
Why is ABI falsely elevated in diabetes?
In patients with diabetes, chronic kidney disease, or long-term hypertension, the arterial walls calcify (medial calcinosis). These calcified arteries cannot be compressed by the blood pressure cuff, resulting in falsely high ankle pressures and ABI values above 1.40. When this occurs, clinicians use alternative tests: Toe-Brachial Index (TBI) — a TBI below 0.70 indicates PAD since toe vessels resist calcification; pulse volume recordings; or duplex ultrasound.
How is the ABI test performed clinically?
Clinical ABI measurement: patient rests supine for 10 minutes; blood pressure cuffs are placed on both arms and both ankles; a handheld Doppler probe (8–10 MHz) is used to detect arterial flow; systolic pressure is recorded for both brachial arteries (use the highest) and both ankle arteries (dorsalis pedis and posterior tibial, use highest per limb); ABI = highest ankle ÷ highest brachial. The test takes about 15–20 minutes and requires no special preparation.
Can ABI predict cardiovascular risk?
Yes. ABI is a validated cardiovascular risk marker. An ABI below 0.90 doubles the 10-year risk of major cardiovascular events (heart attack, stroke, cardiovascular death) compared to normal ABI, independent of traditional Framingham risk factors. The 2013 ACC/AHA guidelines include ABI screening as a Class IIa recommendation for intermediate cardiovascular risk patients to help reclassify risk when risk-based treatment decisions are uncertain.
What treatments are used for low ABI / PAD?
Treatment for PAD based on ABI severity: Mild-Moderate PAD: supervised exercise therapy (strongest evidence), antiplatelet therapy (aspirin or clopidogrel), statin therapy (LDL < 70 mg/dL goal), ACE inhibitor, smoking cessation (single most impactful intervention), blood pressure and diabetes control. Moderate-Severe PAD: above plus vascular specialist evaluation for revascularization (endovascular or surgical). Critical limb ischemia: urgent revascularization to prevent amputation.