𦡠ABI Calculator
Screen for peripheral artery disease from blood pressure readings.
Ankle-brachial index
For informational purposes only, not medical advice. Consult a healthcare professional.
The ankle-brachial index is the simplest reliable screen for peripheral artery disease: divide the systolic pressure at the ankle by the systolic pressure in the arm. Healthy leg arteries deliver full pressure to the ankle, so the ratio sits around 1.0 to 1.4. Narrowed arteries drop the ankle pressure, and the ratio falls with the severity of the blockage.
This calculator takes the highest ankle pressure per leg and the higher of the two arm pressures, computes each leg's ABI, and interprets the result using American Heart Association categories. It takes two minutes with a blood pressure cuff and a Doppler probe.
How to use this calculator
Measure systolic pressures with the patient lying flat after 10 minutes of rest: both arms, and each ankle (use the higher of the dorsalis pedis and posterior tibial readings per leg).
Enter the highest ankle systolic for the right and left legs.
Enter both arm systolics. The calculator uses the higher arm as the denominator for both legs.
Read each leg's ABI and the interpretation for the worse leg, which drives clinical decisions.
The formula and categories
Each leg gets its own index, and both share the same denominator: the higher brachial systolic. Using the higher arm pressure avoids underestimating disease when one arm has subclavian stenosis.
An ABI of 0.90 or less is about 90 percent sensitive and 95 percent specific for angiogram-confirmed peripheral artery disease. Values above 1.40 do not mean superb circulation; they mean calcified, incompressible vessels, common in diabetes and kidney disease, and the test cannot be interpreted.
Worked example
Right ankle 110, left ankle 118, right arm 120, left arm 122. The denominator is the higher arm: 122. Right ABI = 110/122 = 0.90. Left ABI = 118/122 = 0.97. The right leg sits exactly at the PAD threshold and the left is borderline, a pattern that fits early bilateral disease and deserves risk-factor review and possibly an exercise ABI.
Now a clearer case: ankle 70, arms 130 and 128. ABI = 70/130 = 0.54, mild-to-moderate PAD trending severe. At this level, claudication (calf pain with walking that eases with rest) is typical, and vascular imaging is usually next.
What your result means
1.00 to 1.40: normal. 0.91 to 0.99: borderline; repeat the measurement and look hard at smoking, diabetes, and cholesterol. 0.90 or below: peripheral artery disease until proven otherwise. Below 0.40: severe disease, with risk of rest pain, non-healing wounds, and limb loss.
PAD is also a window into the whole arterial tree: people with a low ABI carry two to three times the risk of heart attack and stroke, even without leg symptoms. That is why guidelines treat a PAD diagnosis like a coronary diagnosis for prevention. Track your arm pressures with our blood pressure checker, and assess overall cardiac risk factors alongside.
When ABI misleads
Calcified vessels in diabetes, chronic kidney disease, and advanced age can fake a normal or high ABI while disease lurks underneath. If the ABI is above 1.40 or the clinical suspicion is high despite a normal result, the toe-brachial index (TBI) is the next step, since toe vessels calcify less. Exercise ABI, measuring pressures after treadmill walking, unmasks disease that resting pressures hide.
Technique matters too. Cuffs must fit the ankle, the patient must be supine and rested, and pressures should be taken with a Doppler probe, not just a standard cuff, because ankle pulses are harder to hear. A rushed bedside attempt can easily be off by 0.1, which is the difference between borderline and abnormal.
After a low ABI: what treatment looks like
A low ABI usually starts with risk-factor overhaul, not surgery. Smoking cessation is the single highest-yield move: continued smoking roughly doubles amputation risk. High-intensity statin, blood pressure control, and diabetes management follow, treating PAD like the coronary-equivalent disease it is. Antiplatelet therapy, usually aspirin or clopidogrel, is standard for symptomatic PAD.
Supervised exercise therapy is the surprise star. Structured walking programs, typically 30 to 45 minutes three times a week for 12 weeks, can double pain-free walking distance, outperforming many procedures for claudication. Medicare covers it for PAD, which tells you how strong the evidence is.
Revascularization enters for severe claudication that limits life despite exercise, or for critical limb ischemia: rest pain, non-healing wounds, or gangrene. Options run from angioplasty and stenting to bypass surgery, chosen by anatomy and surgical risk. The goal is always the same: keep the patient walking on their own feet.
Exercise ABI: catching what rest misses
Some patients have classic claudication with a normal resting ABI. Arterial narrowing that is mild at rest becomes flow-limiting during exercise, when leg muscles demand far more blood. The exercise ABI captures this: measure pressures at rest, have the patient walk on a treadmill until symptoms force a stop, then repeat the ankle pressures immediately.
A drop of more than 20 percent in ankle pressure after exercise, or an ABI fall of 0.15 or more, unmasks disease the resting test missed. Recovery time matters too: pressures that take more than a few minutes to return to baseline suggest significant stenosis. Vascular labs run this routinely, and it is the tiebreaker for borderline resting results with convincing symptoms.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What is a normal ankle-brachial index?
1.00 to 1.40. Values in this range suggest no significant large-vessel narrowing in the leg. The test compares ankle systolic pressure to the higher arm systolic pressure.
What ABI indicates peripheral artery disease?
0.90 or below. This threshold is about 90 percent sensitive for PAD confirmed on imaging. Below 0.40 indicates severe disease.
What does an ABI above 1.4 mean?
Noncompressible, calcified arteries, common in diabetes and kidney disease. The ABI cannot be interpreted; a toe-brachial index is used instead.
How is the ABI test performed?
The patient lies flat for 10 minutes, then systolic pressures are measured in both arms and at each ankle (dorsalis pedis and posterior tibial) with a Doppler probe. Each leg's ABI uses its highest ankle pressure over the higher arm pressure.
Can I calculate ABI at home?
Only roughly. Proper technique needs a Doppler probe and correctly sized cuffs, and home cuffs often misread ankle pressures. A clinic measurement is worth it for an accurate result.
What are symptoms of peripheral artery disease?
Calf or thigh pain with walking that eases with rest (claudication), leg numbness, cold feet, slow-healing sores, and in severe cases pain at rest. Many people with PAD have no leg symptoms at all.
Does PAD increase heart attack risk?
Yes, substantially. PAD signals systemic atherosclerosis, so a low ABI roughly doubles to triples the risk of heart attack and stroke. Prevention (statin, blood pressure control, smoking cessation, walking therapy) targets the whole system.
What is the difference between ABI and TBI?
ABI uses ankle pressures; TBI (toe-brachial index) uses toe pressures. Toe arteries calcify less, so TBI stays reliable in diabetes and kidney disease when ABI reads falsely high. Normal TBI is 0.70 or above.
How often should ABI be rechecked?
After a PAD diagnosis, typically every 1 to 2 years or when symptoms change. After revascularization, surveillance follows the vascular team's schedule.
Can exercise improve a low ABI?
Supervised walking programs improve walking distance and symptoms markedly, though the ABI number itself may barely change. The benefit comes from collateral vessels and muscle efficiency, not from reopening the blocked artery.