Ankle-Brachial Index: A simple test called an ankle-brachial index (ABI) often is used as an initial non-invasive test to diagnose peripheral arterial disease (also called PAD), artery blockages caused by atherosclerotic plaque, which very often affects the arteries of the legs. An ABI test compares the blood pressures in your ankles to the blood pressure measurements in your arms. It can show whether PAD is affecting your limbs, but it won’t show which blood vessels are narrowed or blocked. Further testing is necessary to do that, but if the ABI is normal, it makes it less likely that you have PAD.