The ankle-brachial ratio (ABI) is an abbreviation for ankle brachial index, also known as the ankle-brachial index, and is one of the most commonly used and simplest tests in vascular surgery. The ratio between ankle artery pressure and brachial artery pressure is obtained by measuring the systolic pressure of the posterior tibial or anterior tibial artery in the ankle and the brachial artery in the arm. Because the arterial pressure in the lower extremity is usually higher than that in the upper extremity, the ankle-brachial index is usually greater than 1.0 in a normal person at rest; in patients with intermittent claudication, the ankle-brachial index is mostly 0.5 to 0.9, while in patients with resting pain, it is often less than 0.5, and it is generally believed that such patients are at risk of amputation if they are not treated actively.