The ankle-brachial index (ABI) is the ratio of systolic blood pressure (SBP) in the ankle to that in the brachial artery. Winsor first described this index in 1950 as a quick, non-invasive, and inexpensive method to diagnose peripheral artery disease (PAD). Later, ABI was used as an effective indicator of atherosclerosis at other vascular sites.
It also serves as a prognostic marker for cardiovascular events and functional impairment in the absence of PAD symptoms. ABI is calculated as: ABI = Ankle systolic pressure/brachial systolic pressure Precautions should be taken to maintain a minimal (less than 10 mmHg) interarm systolic pressure gradient during a routine examination.
