The ankle-brachial index test is a quick, non-invasive way to assess your risk for peripheral artery disease, a condition in which the arteries in your legs and ankles are narrowed. People with peripheral artery disease are at a higher risk of heart attack, stroke and poor circulation. The ankle-brachial index test compares your blood pressure measured at your ankle with your blood pressure measured at your arm. A low ankle-brachial index number can indicate narrowing or blockage of the arteries in your legs, leading to circulatory problems, heart disease or stroke.