A simple, inexpensive method to assess the degree of vascular insufficiency in peripheral vascular disease. It is calculated by measuring the resting (and post-exercise if necessary) systolic blood pressures in the ankle and arm.

The highest of four measurements in the ankles and feet (posterior tibial and dorsalis pedis arteries) is divided by the higher of two brachial artery measurements.

Normal ABI ratio is 1 - 1.3 (pressure is higher in the ankle than the arm). Values > 1.3 suggest a noncompressible, calcified vessel.

ABI < 0.9 is associated with at least 50% stenosis in one or more major vessels.

Specifically,
0.4 - 0.9: arterial obstruction, claudication
< 0.4: advanced ischemia