Originally described by Winsor in 1950, the ABI was initially proposed for the noninvasive diagnosis of lower-extremity peripheral artery disease (PAD). Later, it was shown that the ABI is an indicator of atherosclerosis at other vascular sites and can serve as a prognostic marker for cardiovascular events and functional impairment, even in the absence of symptoms of PAD
The ABI measurement is based on the ratio of the lowest ankle blood pressures divided by the highest arm blood pressure. Recent studies suggest the use of low ankle pressure ABI as the method for calculating the ABI due to its better sensitivity. It is simply a mathematical division based on the accuracy of the blood pressure measurements. TBL-ABI complies with the procedure for measuring the ABI with 2 blood pressure measurements at each ankle (dorsalis pedis and tibial artery) and measurements at the right and left arm.