Ankle-Brachial Index (ABI) Calculator

How to Use This Calculator

1. Enter right and left ankle systolic pressures and right and left brachial systolic pressures.
2. ABI for each side is calculated as ankle SBP ÷ highest brachial SBP.
3. The lowest ABI drives the interpretation and PAD severity category.
4. Use the Toe-Brachial Index tab if ABI > 1.40 (non-compressible vessels).

Formula

Example

Frequently Asked Questions

• What does the ankle-brachial index measure? ▼
  The ankle-brachial index (ABI) is the ratio of the systolic blood pressure measured at the ankle to the systolic blood pressure measured at the brachial artery (arm). It is the primary non-invasive screening test for peripheral artery disease (PAD) of the lower extremities. The ABI is calculated by dividing the highest ankle pressure (posterior tibial or dorsalis pedis) by the highest brachial pressure. In healthy arteries without significant stenosis, blood pressure at the ankle should be equal to or slightly higher than arm pressure because of the column of blood from the heart — so a normal ABI is 1.00 to 1.40. When atherosclerosis causes narrowing of the iliac, femoral, popliteal, or tibial arteries, blood pressure drops distal to the stenosis, and the ABI falls below 1.00. An ABI of 0.71-0.90 indicates mild PAD, 0.41-0.70 moderate PAD (typically associated with claudication symptoms), and ≤0.40 severe PAD with risk of critical limb ischemia. An ABI above 1.40 indicates arterial calcification (non-compressible vessels), common in diabetes and chronic kidney disease, and is actually a risk marker — the toe-brachial index is needed in these patients.
• When should I get an ABI test? ▼
  The ABI test is recommended as a PAD screening tool in specific high-risk populations. The AHA/ACC 2016 PAD guideline and ESC PAD guidelines recommend ABI measurement in: all patients aged ≥70 years (regardless of symptoms); patients aged 50-69 with diabetes or smoking history; patients aged < 50 with diabetes plus one or more additional PAD risk factor (obesity, hypertension, dyslipidemia); patients with suspected PAD symptoms (exertional leg pain, non-healing wounds, abnormal lower extremity pulse examination); and patients being evaluated for cardiovascular risk (since low ABI is a CAD risk equivalent, meaning it elevates overall cardiovascular event risk similar to established coronary artery disease). The ABI is not recommended as a screening test in the general low-risk population without symptoms or risk factors. Patients with claudication, rest pain, non-healing foot ulcers, or gangrene should be evaluated with ABI as part of their initial workup. The test takes about 15-20 minutes, requires only a standard sphygmomanometer and Doppler probe, and can be performed in any outpatient setting.
• What is a normal vs abnormal ABI? ▼
  The ABI classification system divides results into five meaningful categories. An ABI greater than 1.40 is considered abnormal high — this indicates non-compressible, calcified arteries (typically due to diabetes mellitus or chronic kidney disease). These patients cannot be assessed with standard ABI and require toe-brachial index instead; paradoxically, this finding carries increased cardiovascular mortality risk. An ABI of 1.00-1.40 is normal, indicating no significant arterial obstruction. An ABI of 0.91-0.99 is borderline and warrants consideration of post-exercise ABI testing — a drop of ≥20% post-exercise is diagnostic for occult PAD in symptomatic patients who have normal resting ABI. An ABI of 0.71-0.90 indicates mild PAD; many patients in this range are asymptomatic, but limb and cardiovascular risk is elevated. An ABI of 0.41-0.70 indicates moderate PAD, corresponding to the range where most patients with claudication symptoms are found. An ABI ≤ 0.40 indicates severe PAD — patients in this range are at risk for critical limb-threatening ischemia, defined as rest pain, non-healing tissue loss, or gangrene, and require urgent vascular evaluation.
• Why does ABI predict cardiovascular mortality? ▼
  A low ABI is a powerful predictor of cardiovascular mortality that operates through two mechanisms. First, it is a direct indicator of systemic atherosclerotic burden: patients who have significant atherosclerosis in their leg arteries (reflected by low ABI) almost certainly have atherosclerosis elsewhere — in the coronary arteries, carotid arteries, renal arteries, and mesenteric arteries. The underlying disease process is the same. Multiple large-scale studies have consistently shown that an ABI < 0.90 is associated with 2-3 times higher risk of cardiovascular events compared to patients with normal ABI, after adjusting for traditional risk factors. Second, a low ABI identifies patients who are often not recognized as high-risk because they lack symptoms of coronary artery disease — screening with ABI in primary prevention populations reclassifies a substantial proportion of patients from intermediate to high cardiovascular risk, which then triggers more intensive risk factor modification (statins, antiplatelet therapy, ACE inhibitor or ARB for hypertension). The 2016 AHA/ACC PAD guideline explicitly classifies PAD as a "ASCVD risk equivalent," meaning PAD patients should receive the same secondary prevention therapy as post-MI patients.
• Can I do an ABI at home? ▼
  A technically accurate ABI measurement requires specialized equipment and training that is not available for home use. The standard clinical ABI uses a handheld Doppler probe (typically 8 MHz) to detect blood flow sounds at the posterior tibial and dorsalis pedis arteries in each ankle, combined with blood pressure cuffs. The Doppler probe is essential because simple pulse palpation is unreliable in PAD patients (reduced pulses are the disease marker), and standard automated blood pressure cuffs cannot accurately detect ankle pressures when arteries are diseased. Using a standard home blood pressure cuff without Doppler on the ankle can give readings, but these will often be unreliable, particularly in the patients who most need accurate ABI (those with calcified or stenotic arteries). Some specialized home ABI devices have been developed (using photoplethysmography or automated Doppler), but these are generally not consumer devices and are primarily used in clinical research. For practical purposes, ABI should be performed by a trained healthcare provider using Doppler equipment. However, patients can monitor their symptoms at home — progressive decrease in walking distance, onset of rest pain, or new foot wounds — and report these to trigger formal ABI testing.

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