The ankle-brachial pressure index (ABPI) is the ratio of the systolic blood pressure at the ankle (highest of the dorsalis pedis and posterior tibial artery pressures) to the systolic blood pressure in the upper arm (brachial artery pressure).
ABPI is measured on the same side of the body (left ankle compared with left upper arm).
Lower blood pressure in the leg than the arm (a low ABPI, less than 1) suggests blocked arteries due to PAD.