Calculate the ankle-brachial index (ABI) for PAD screening. Interprets severity, flags non-compressible arteries, inter-arm differences, and Rutherford classification.
The Ankle-Brachial Index (ABI) Calculator evaluates peripheral arterial disease (PAD) severity by computing the ratio of ankle systolic blood pressure to brachial systolic blood pressure. The ABI is the most widely used non-invasive screening test for lower extremity PAD, recommended by ACC/AHA guidelines for at-risk populations.
The test uses a handheld continuous-wave Doppler to measure systolic pressures in both brachial arteries and in the dorsalis pedis and posterior tibial arteries of each ankle. The highest brachial pressure is used as the denominator, and the highest ankle pressure on each side is used as the numerator. An ABI of 1.0-1.4 is normal; below 0.9 indicates PAD, and above 1.4 suggests non-compressible, calcified arteries often seen in diabetes and CKD.
This calculator computes both right and left ABI, identifies the overall (lower) value, flags significant inter-arm blood pressure differences (which may indicate subclavian stenosis), and maps results to the Rutherford classification for peripheral arterial disease. It also alerts when non-compressible arteries make ABI unreliable and toe-brachial index (TBI) is needed.
The ABI is a simple screening test for peripheral arterial disease and can identify reduced lower-limb perfusion before symptoms become advanced. This calculator automates the ratio, highlights non-compressible arteries, and summarizes the result in a clinical context.
ABI = Higher ankle systolic pressure (DP or PT) / Higher brachial systolic pressure Normal: 1.00-1.40 | Borderline: 0.91-0.99 | Mild PAD: 0.71-0.90 | Moderate PAD: 0.41-0.70 | Severe PAD: ≤0.40 | Non-compressible: >1.40
Result: Right ABI 0.79, Left ABI 0.82 — Mild PAD
Both ABIs fall in the mild PAD range (0.71-0.90). Higher brachial = 140; the right ankle (higher = 110) gives 110/140 = 0.79. The page reports the ratio and severity band; symptoms still need to be assessed separately.
Peripheral arterial disease affects approximately 8-12% of adults aged 60+ and over 20% of those aged 80+. Despite its high prevalence, PAD is underdiagnosed — up to 50% of patients with PAD are asymptomatic. The ABI provides a quick, inexpensive method to identify these silent cases before complications like critical limb ischemia, amputation, or cardiovascular events occur.
Beyond diagnosing PAD, the ABI is a powerful predictor of overall cardiovascular risk. A low ABI indicates systemic atherosclerosis and is associated with 2-6× increased risk of coronary events, stroke, and cardiovascular death. Many guidelines recommend reclassifying patients with low ABI into higher cardiovascular risk categories for more aggressive prevention.
When resting ABI is borderline (0.91-0.99) or symptoms suggest PAD despite normal resting ABI, exercise testing provides additional diagnostic sensitivity. After standardized treadmill exercise, a decrease in ankle pressure of >20% strongly suggests hemodynamically significant proximal arterial stenosis that may not be apparent at rest.
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This page follows the standard ankle-brachial index method by taking the higher of the two brachial systolic pressures as the denominator, then dividing the higher ankle artery pressure on each side by that brachial value. It reports the right ABI, left ABI, and the lower overall ABI, which is the number usually used for PAD screening and severity framing. It also flags ABI values above 1.40 as potentially non-compressible and notes a clinically important inter-arm systolic difference.
The result is meant to support bedside vascular screening rather than replace formal Doppler technique or vascular-lab interpretation. Non-compressible arteries, rest pain, tissue loss, and discordance between symptoms and ABI should prompt follow-up with toe pressures, duplex testing, exercise ABI, or other vascular evaluation rather than relying on the resting ratio alone.
An ABI ≤ 0.90 is diagnostic for PAD with high sensitivity (95%) and specificity (almost 100%). Values 0.91-0.99 are borderline and warrant monitoring.
The higher arm pressure helps avoid underestimating PAD when one brachial artery is narrowed. Using the lower arm could make the ABI appear falsely normal.
It indicates non-compressible, calcified arteries — the cuff cannot compress them to occlude flow. This is common in diabetes and CKD. Toe-brachial index (TBI) should be used instead.
ABI can be falsely elevated due to medial arterial calcification (Mönckeberg sclerosis). Up to 30% of diabetic patients may have non-compressible arteries. TBI is preferred in this population.
A difference >10 mmHg suggests possible subclavian artery stenosis and is independently associated with increased cardiovascular risk.
ACC/AHA recommends ABI screening for adults ≥65, adults ≥50 with diabetes or a smoking history, anyone with exertional leg symptoms, and patients with known atherosclerotic disease in other vascular beds.
Next steps may include duplex ultrasound, exercise ABI testing, segmental pressures, and CT or MR angiography depending on severity and clinical context.