- Measure the brachial (arm) systolic pressure in both arms with a Doppler probe and enter each value (mm Hg). The higher of the two arms becomes the brachial reference.
- For each leg, measure the systolic pressure over the dorsalis pedis (DP) and the posterior tibial (PT) arteries with the Doppler. Enter whichever you obtained — at least one ankle pressure per leg is required.
- Each leg's ABI = (the higher of that leg's DP and PT) ÷ the brachial reference. The overall ABI is the lower of the two legs — the most abnormal limb drives the diagnosis.
- Results classify per the AHA bands: >1.40 non-compressible, 1.00–1.40 normal, 0.91–0.99 borderline, 0.41–0.90 mild-to-moderate PAD, ≤0.40 severe PAD.
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When to Use
Use the ABI to screen for lower-extremity peripheral artery disease (PAD) and to refine cardiovascular risk. It is indicated in patients with exertional leg symptoms (claudication), non-healing foot wounds or rest pain, absent or diminished pedal pulses, and as risk-stratification in high-risk groups — notably patients with diabetes and/or chronic kidney disease, smokers, and those aged ≥65 (or younger with multiple risk factors). An abnormal ABI both diagnoses PAD and marks generalized atherosclerosis.
Appropriate population
Adults being evaluated for claudication, suspected PAD, non-healing lower-limb wounds, or critical limb ischemia, and high-risk patients screened for occult PAD — especially the diabetic-CKD population, in whom PAD is common, often silent, and a powerful cardiovascular and limb-loss risk marker.
When NOT to rely on it
A resting ABI above 1.40 (non-compressible / medially calcified arteries) is uninterpretable for PAD — common in diabetes, CKD, and ESKD because of medial (Mönckeberg) calcification. In that situation a normal or high ABI does not exclude PAD; obtain a toe-brachial index (TBI) or other imaging instead. A normal resting ABI also does not exclude PAD when symptoms are exertional — consider exercise ABI testing.
Pearls & Pitfalls
The lower leg drives the diagnosis
Each leg's ABI uses the higher of its DP and PT pressures over the higher of the two arm pressures. The overall ABI is the lower of the two legs, because the more abnormal limb is what defines disease — a normal contralateral ABI does not reassure you about a symptomatic leg. Always interpret each leg on its own as well as the overall value.
Beyond the legs — a CV risk marker
ABI is not just a limb test: a low ABI independently predicts myocardial infarction, stroke, and cardiovascular death. An abnormal value should trigger global risk-factor modification — high-intensity statin, antiplatelet therapy, blood-pressure and glucose control, and smoking cessation — regardless of whether the patient has leg symptoms.
Pitfalls
(1) Non-compressible arteries (ABI >1.40) are falsely elevated from medial calcification — endemic in diabetes, CKD, and ESKD — and can mask true PAD; use the toe-brachial index (TBI) instead. (2) A normal resting ABI does not exclude PAD in patients with exertional symptoms — consider exercise testing. (3) Garbage in, garbage out: a properly performed Doppler measurement (not palpation, not an automated cuff alone) is essential. (4) The overall ABI must be the lower leg, not an average — averaging hides unilateral disease.
Why Use It
The ABI is a simple, inexpensive, non-invasive test that does two jobs at once: it diagnoses lower-extremity peripheral artery disease and it stratifies a patient's overall cardiovascular risk. PAD is frequently silent — especially in people with diabetes and CKD, who may have neuropathy that blunts claudication — so an objective bedside ratio catches disease that history and pulse palpation miss. Because the same atherosclerotic process affects the coronary and cerebral beds, a reduced ABI flags patients who stand to benefit most from aggressive risk-factor modification, and a severely low value (≤0.40) identifies critical limb ischemia that warrants urgent vascular referral. In a nephrology practice rich in diabetic-CKD patients, the ABI — paired with awareness that medial calcification falsely elevates it — is a high-yield, guideline-endorsed screen.
Ankle-Brachial Index (ABI)
Enter the systolic pressures (mm Hg). The brachial reference is the higher of the two arms; each leg uses the higher of its dorsalis pedis (DP) and posterior tibial (PT) pressures. Results appear once both arm pressures and at least one ankle pressure per leg are entered.
⚕ AHA method (Aboyans 2012): brachial reference = higher arm systolic; each leg ABI = higher of that ankle's DP/PT ÷ brachial reference; overall ABI = the lower of the two legs. An ABI >1.40 is non-compressible (calcified) and uninterpretable for PAD — obtain a toe-brachial index. For licensed clinicians; not a substitute for individualized assessment.
Next Steps
Use the per-leg and overall ABI to classify peripheral arterial status and direct the next move.
- Normal (1.00–1.40): PAD unlikely by resting ABI. If exertional symptoms persist, consider exercise (post-treadmill) ABI testing.
- Borderline (0.91–0.99): early/equivocal — recheck, consider exercise ABI, and address cardiovascular risk factors.
- Mild-to-moderate PAD (0.41–0.90): confirms PAD. Start guideline-directed therapy — high-intensity statin, antiplatelet, blood-pressure and glucose control, smoking cessation, and supervised exercise; refer to vascular medicine for symptomatic disease.
- Severe PAD (≤0.40): critical limb ischemia range — urgent vascular surgery / interventional referral for revascularization assessment, especially with rest pain or tissue loss.
- Non-compressible (>1.40): result is uninterpretable for PAD (medial calcification, common in diabetes & CKD). Obtain a toe-brachial index (TBI) or further imaging; do not assume the limb is disease-free.
- Pair with global CV risk estimation using the AHA PREVENT calculator and optimize blood-pressure targets.
Evidence & References
Formula
| Quantity | Formula |
|---|---|
| Brachial reference | higher of (right arm systolic, left arm systolic) |
| Right ABI | max(right DP, right PT) ÷ brachial reference |
| Left ABI | max(left DP, left PT) ÷ brachial reference |
| Overall ABI | lower of (right ABI, left ABI) — most abnormal limb |
Interpretation (AHA 2012)
| ABI | Interpretation |
|---|---|
| >1.40 | Non-compressible / calcified arteries — falsely elevated (diabetes, CKD/ESKD); obtain toe-brachial index |
| 1.00–1.40 | Normal |
| 0.91–0.99 | Borderline |
| 0.41–0.90 | Mild-to-moderate PAD |
| ≤0.40 | Severe PAD (critical limb ischemia range) |
The ABI is a validated, guideline-endorsed screen for lower-extremity PAD and an independent marker of generalized atherosclerosis and cardiovascular risk. In diabetes and CKD, medial calcification raises the ABI above 1.40 and a toe-brachial index is substituted.
References
- Aboyans V, Criqui MH, Abraham P, et al. Measurement and interpretation of the ankle-brachial index: a scientific statement from the American Heart Association. Circulation. 2012;126(24):2890–2909.
- Gerhard-Herman MD, Gornik HL, Barrett C, et al. 2016 AHA/ACC guideline on the management of patients with lower extremity peripheral artery disease. Circulation. 2017;135(12):e726–e779.
- Aboyans V, Ricco JB, Bartelink MEL, et al. 2017 ESC guidelines on the diagnosis and treatment of peripheral arterial diseases. Eur Heart J. 2018;39(9):763–816.
