The ankle-brachial index (ABI) test, sometimes called the arm-ankle index, is useful in determining a person’s risk for peripheral artery disease (PAD), a condition in which the arteries in the legs and ankles have narrowed. Patients age 50 and over, who smoke, are overweight, or have been diagnosed with diabetes, high blood pressure or high cholesterol have a significantly higher risk of developing PAD and can benefit from an ABI. The test can also be helpful by establishing the progression of the disease or the effectiveness of treatment.
The test is a simple, non-invasive procedure in which blood pressure measurements are taken at both the arm and the ankle. It is both reliable and comparatively inexpensive. The patient will lie quietly for a short time to allow the blood pressure to stabilize before the test begins. Normal systolic blood pressure is taken first, using blood pressure cuffs. Once the cuffs are deflated, a Doppler ultrasound device is used to measure blood pressure. To obtain the ABI measurement for each leg, the ankle systolic pressures are divided by the highest arm pressure, .95 to 1.2 is considered a normal range. The test may be repeated after having the patient walk on a treadmill for about five minutes. A slight drop in ABI measurement after walking on the treadmill is an excellent indicator of PAD.
While ankle-brachial index testing is an extremely reliable predictor, some patients with conditions such as diabetes, kidney disease and elderly patients may have rigid blood vessels. The physician may choose to use an alternate procedure, such as a toe-brachial index, where the big toe is used rather than the ankle. The test takes only 10 to 15 minutes and can be done at your physician�s office.
Physicians are able to use the ABI measurements to accurately predict severity of disease or likelihood of future problems. An index of less than 0.90 means blood is having difficulty reaching the legs and feet, while 0.41 to 0.90 indicates mild to moderate PAD, and 0.4 or lower indicates severe disease. ABI allows physicians to help their patients keep risk factors low in order to prevent the effects of the disease from progressing. For those at high risk, the test could be repeated periodically.