Ankle-brachial index test

This test is done by measuring blood pressure at the ankle and in the arm while a person is at rest. Measurements are usually repeated at both sites after 5 minutes of walking on a treadmill.

The ankle-brachial index (ABI) result is used to predict the severity of peripheral arterial disease (PAD). A slight drop in your ABI with exercise means that you probably have PAD. This drop may be important because PAD can be linked to a higher risk of heart attack or stroke.

This test is done to screen for peripheral arterial disease of the legs. It is also used to see how well a treatment is working (such as medical treatment, an exercise program, angioplasty, or surgery).

The ABI result can help diagnose peripheral arterial disease (PAD). A lower ABI means you might have PAD. A slight drop in the ABI with exercise, even if you have a normal ABI at rest, means that you probably have PAD.

Normal

A normal resting ankle-brachial index is 1 or 1.1. This means that your blood pressure at your ankle is the same or greater than the pressure at your arm, and suggests that you do not have significant narrowing or blockage of blood flow.

Abnormal

A resting ankle-brachial index of less than 1 is abnormal. If the ABI is:

• Less than 0.95, significant narrowing of one or more blood vessels in the legs is indicated.
• Less than 0.8, pain in the foot, leg, or buttock may occur during exercise (intermittent claudication).
• Less than 0.4, symptoms may occur when at rest.
• 0.25 or below, severe limb-threatening PAD is probably present.

You may experience leg pain during the treadmill portion of the test if you have peripheral arterial disease (PAD).

Undiagnosed arterial disease in the arms can cause inaccurate test results.

Blood pressure readings may not be accurate when the blood vessel being measured is hardened by calcium (calcified). Arteries may calcify more than usual if you have diabetes or kidney problems (renal insufficiency).¹

A very abnormal ABI test result may require more testing to determine the location and severity of PAD that might be present.

Complete the medical test information form (PDF)(What is a PDF document?) to help you prepare for this test.

Citations

1. Creager MA, Libby P (2004). Peripheral arterial diseases. In DP Zipes et al., eds., Braunwald's Heart Disease, 7th ed., pp. 1437–1461. Philadelphia: Elsevier Saunders.