In addition, a low ankle-brachial index may mean that your legs and feet are not getting as much blood as they need. Reduced blood flow may provoke pain and numbness. It frequently affects the vessels that carry blood to the legs. In peripheral artery disease, plaque builds up in the arteries. If the ratio is less than 0.9, it may mean that an individual has peripheral artery disease (PAD) in the blood vessels of the legs. The result is the ankle-brachial index (ABI). Healthcare providers calculate the ABI (ankle-brachial index) by dividing the blood pressure in an artery in your ankle by the blood pressure in an artery in your arm. The ankle-brachial index (ABI) is an uncomplicated test that contrasts the blood pressure in the superior and lower extremities.