What is an ankle-brachial index test?

A simple test, called the ankle-brachial index, or ABI, can quickly and painlessly determine if you likely have peripheral artery disease (PAD), which means blockages in the blood vessels leading to your legs. PAD, also referred to as peripheral vascular disease (PVD), can cause discomfort or weakness while walking and, if severe and left untreated, can potentially lead to amputation of the leg or foot.
Anthony L. Komaroff, MD
Internal Medicine
The ankle-brachial index (ABI) is the highest blood pressure recorded at the ankle divided by the highest pressure recorded at the brachial artery (in the arm). The normal range is between 0.90 and 1.30. An index under 0.90 means that blood is having a hard time getting to the legs and feet: 0.41 to 0.90 indicates mild to moderate peripheral artery disease; 0.40 and lower indicates severe disease. The lower the index, the higher the chances of leg pain while exercising or of limb-threatening low blood flow. An ABI over 1.30 is usually a sign of stiff, calcium-encrusted arteries. These often occur in people with diabetes or chronic kidney disease. In such cases, blood pressure should be measured at the toe, where arteries are less likely to be rigid.

The ABI also offers information about general cardiovascular health. An analysis in The Journal of the American Medical Association of studies involving nearly 50,000 men and women showed that a low ankle-brachial index (under 0.90) doubled the chances of having a heart attack or stroke or dying of heart disease over a 10-year period. The researchers suggested that the ABI could improve the accuracy of the widely used Framingham risk score.

ABI is an acronym for Ankle Brachial Index - a simple, quick and painless test your doctor can use to check for PAD. Your doctor will use a traditional blood pressure cuff and a special ultrasound device to compare the blood pressure in your ankle to that of the blood pressure in your arm artery (the brachial artery). The comparison gives your doctor an indication of how well the blood is flowing in your legs. It is so simple it does not even require your skin to be punctured. Commonly these tests are done either at rest or after exercise on a treadmill.

It is important to understand that an ABI test cannot show which blood vessels are narrowed or blocked. It gives your doctor an idea of how much blockage is present in the legs and if you are in need of further testing, such as a CT or MRI scan or an angiogram.

An ankle-brachial index (ABI) test is one of the most common tests used to diagnose peripheral vascular disease (PVD). An ABI test compares the blood pressure in your ankle and your arm. Here’s what happens during an ABI test:
  • Getting ready. You’ll change into a gown and lie down on an exam table.
  • Blood pressure cuffs. A technician will place blood pressure cuffs on your arms and ankles and inflate the cuffs.
  • Ultrasound. As the cuffs deflate, a technician will hold an ultrasound device called a transducer against each ankle and arm. The device uses high-frequency sound waves to measure the blood pressure in each area.
  • Ratio. The ankle blood pressures will be divided by the highest arm pressure to create an ABI ratio. A ratio lower than normal means you probably have peripheral arterial disease (PAD).
  • Treadmill exercise, then a second measurement (optional). Depending on your situation, you might exercise on a treadmill. You will then have another ABI test. Note: If you don’t feel well during the test, ask the technician to stop the treadmill. Wait for the treadmill to stop completely before you step off it.
An ankle brachial index (ABI) is a noninvasive test that screens for peripheral arterial disease. It is a measurement of blood pressure in the legs compared to the blood pressure in the arms. During this test, blood pressure cuffs are placed on the arms and legs. The ABI screening helps evaluate the amount of blood flow to the legs and feet, which is decreased in a person with peripheral arterial disease. The screening takes only a few minutes.