Ankle-Brachial Index Calculator
Enter systolic pressures obtained by Doppler for dorsalis pedis and posterior tibial arteries along with simultaneous brachial pressures. The calculator uses the highest ankle pressure in each leg divided by the highest brachial pressure to compute ABI.
Right leg pressures (mmHg)
Left leg pressures (mmHg)
Brachial pressures (mmHg)
Use the highest brachial pressure from either arm when calculating ABI for both legs.
How to Use This Calculator
Measure systolic pressures
Using a Doppler probe, record systolic pressures in both dorsalis pedis and posterior tibial arteries and in both brachial arteries.
Input highest values
Enter the recorded pressures. The calculator automatically uses the higher ankle pressure for each leg and the highest brachial pressure for both comparisons.
Review ABI interpretation
Compare calculated ABI values with established thresholds to guide peripheral artery disease screening and the need for vascular referral.
Formula
ABI (per leg) = Highest ankle systolic pressure ÷ Highest brachial systolic pressure
Use dorsalis pedis or posterior tibial pressures measured with Doppler. The larger brachial pressure from either arm is used for both legs.
Full Description
The ankle-brachial index (ABI) is a non-invasive screening tool for peripheral artery disease (PAD). It reflects the ratio between lower extremity and upper extremity systolic pressures, highlighting arterial narrowing or stiffness. ABI assists with PAD diagnosis, cardiovascular risk stratification, and monitoring response to therapy.
Values below 0.9 indicate PAD, while values above 1.4 suggest calcified non-compressible arteries often seen in diabetes and chronic kidney disease. In such cases, toe-brachial index (TBI) is recommended. Clinical correlation with symptoms such as claudication, rest pain, and tissue loss remains essential.
Frequently Asked Questions
Do I measure brachial pressures in both arms?
Yes. Record both sides and use the higher value for ABI calculations. This accounts for subclavian stenosis that can skew results if only one arm is measured.
How should I handle noncompressible arteries?
ABI values > 1.4 suggest arterial calcification. Proceed with toe-brachial index (TBI) or arterial waveform analysis for accurate perfusion assessment.
Can blood pressure cuffs influence accuracy?
Use appropriately sized cuffs placed just above the malleoli and elbows. Undersized cuffs can overestimate pressures; oversized cuffs can underestimate pressures.
When should ABI be repeated?
Repeat ABI testing in patients with PAD risk factors, new symptoms (claudication, rest pain), or to monitor response to interventions such as revascularization or pharmacologic therapy.