ABI Calculator
Calculate Ankle-Brachial Index from ankle and arm blood pressures to screen for PAD. Free online risk assessment with leg-by-leg interpretation and visual charts.
About This Calculator
The Ankle-Brachial Index (ABI) Calculator is a free online screening tool that helps assess your risk of peripheral artery disease (PAD). By comparing the systolic blood pressure measured at your ankles with that measured at your arms, this calculator provides a quick, non-invasive assessment of arterial health in your lower extremities. PAD affects approximately 200 million people worldwide, with prevalence increasing significantly after age 65. Early detection through ABI screening can lead to timely interventions that reduce the risk of heart attack, stroke, and amputation.
The ABI is calculated separately for each leg using the formula: Right ABI = Right Ankle Systolic Pressure / Higher Brachial Systolic Pressure and Left ABI = Left Ankle Systolic Pressure / Higher Brachial Systolic Pressure. Values between 1.0 and 1.4 are considered normal. An ABI below 0.9 indicates PAD with 95% sensitivity and 99% specificity when compared to angiography. Values above 1.4 suggest arterial calcification, which is common in patients with diabetes and chronic kidney disease. The test is performed with the patient resting supine for 5-10 minutes, using a Doppler ultrasound device and a standard blood pressure cuff.
Regional Notes
India: PAD affects approximately 14% of Indians over 60. Guidelines recommend ABI screening for all diabetic patients over 50 years of age. ABI testing typically costs ₹300-800 at diagnostic centers across major cities. The Indian Council of Medical Research (ICMR) includes ABI measurement in its standardized diabetes complication screening protocols.
United States: The USPSTF recommends ABI screening for adults aged 50-75 with cardiovascular risk factors. Medicare Part B covers ABI screening when ordered by a physician for patients with PAD symptoms or elevated risk. The test is widely available at primary care offices, vascular labs, and cardiology clinics. The American Heart Association (AHA) and American College of Cardiology (ACC) include ABI measurement in their PAD clinical practice guidelines.
United Kingdom: NICE guidelines recommend ABI testing for anyone with suspected PAD based on symptoms or risk factors. The NHS offers ABI testing as part of routine vascular assessment in primary care. ABI is also used in cardiovascular risk assessment clinics across the UK, particularly for patients with diabetes and those over 65.
Frequently Asked Questions
What is ABI?
The Ankle-Brachial Index (ABI) is the ratio of ankle systolic blood pressure to brachial (arm) systolic blood pressure. It is the standard non-invasive test for diagnosing peripheral artery disease (PAD). Normal ABI range is 1.0 to 1.4. A value below 0.9 has 95% sensitivity for PAD diagnosis, while a value above 1.4 suggests arterial calcification.
How is ABI interpreted?
ABI interpretation follows a standardized grading system. Above 1.4 indicates arterial calcification requiring vascular specialist consultation. Values between 1.0 and 1.4 are normal. An ABI of 0.9 to 1.0 is borderline acceptable. Values from 0.8 to 0.9 suggest mild PAD, indicating a need to consult your doctor. Moderate PAD is diagnosed at 0.5 to 0.8, and severe PAD below 0.5, both requiring vascular specialist consultation.
Who should get an ABI test?
The ABI test is recommended for adults over 65, current or former smokers, individuals with diabetes, people with high blood pressure or high cholesterol, and those experiencing leg pain or cramping while walking (claudication). The USPSTF recommends screening for at-risk individuals aged 50-75. In India, guidelines recommend screening all diabetics over age 50. The test typically costs between ₹300-800 in India and is covered by most insurance plans in the US and UK.
Can ABI predict cardiovascular risk?
Yes, an ABI below 0.90 is associated with a 2 to 3 times increased risk of cardiovascular events including stroke, myocardial infarction, and cardiovascular death. ABI is recognized as an independent predictor of cardiovascular mortality that adds prognostic value beyond traditional risk factors such as Framingham Risk Score.
What causes false ABI readings?
Non-compressible calcified arteries common in patients with diabetes and chronic kidney disease (CKD) can produce falsely elevated ABI readings above 1.4. For these patients, the Toe-Brachial Index (TBI) is preferred as digital arteries rarely calcify. A normal TBI is above 0.6, while a TBI below 0.6 indicates PAD even when ABI appears normal.
How is the ABI test performed?
The ABI test is performed by a healthcare professional using a Doppler ultrasound device and blood pressure cuff. The patient rests supine for 5-10 minutes. Systolic blood pressure is measured in both brachial arteries (arms) and both posterior tibial and dorsalis pedis arteries (ankles). The highest ankle pressure in each leg is divided by the higher of the two arm pressures to calculate the ABI.
What is the difference between ABI and TBI?
The Toe-Brachial Index (TBI) measures blood pressure in the great toe using a small cuff and Doppler or photoplethysmography. While ABI is the first-line test for PAD, TBI is preferred when arteries are calcified (common in diabetes and CKD). Normal TBI is above 0.6-0.7, while a TBI below 0.6 indicates PAD. TBI is more sensitive for detecting PAD in diabetic populations.
Is ABI test covered by insurance?
In the United States, Medicare and most private insurance plans cover ABI testing for patients with PAD symptoms or risk factors. In the UK, the NHS performs ABI testing as part of routine vascular assessment. In India, ABI testing is available at major hospitals and diagnostic centers, typically costing ₹300-800, and is increasingly covered by health insurance policies for diabetic patients.