Ankle-Brachial Index - Facts

What is Ankle-Brachial Index ('ABI')?

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.

$ABPI_{Leg} = \frac { P_{Leg} }{ P_{Arm} }$

Interpreting an Ankle-Brachial Index result.

No blockage (1.0 to 1.3). An ankle-brachial index number in this range suggests that you probably don't have peripheral artery disease. But if you have certain risk factors, such as diabetes, smoking or a family history of PAD, tell your doctor so that he or she can continue to monitor your risk.
Mild blockage (0.8 to 0.99). If your ankle-brachial index number is less than 1.0, you may have some narrowing of the arteries in your ankle. People with an ankle-brachial index of 0.9 or lower may have the beginnings of peripheral artery disease. Your doctor may then monitor your condition more closely.
Moderate blockage (0.5 to .79). An ankle-brachial index number in this range indicates more significant blockage of your ankle arteries. You may have noticed some pain in your legs or buttocks when you exercise.
Severe blockage (less than 0.5). If your ankle-brachial index number is in this range, your ankle arteries are significantly blocked and you may have pain in your legs even while resting. An ankle-brachial index of less than 0.5 suggests severe peripheral artery disease.

Which clinical guidelines include 'Ankle-Brachial Index' as a suggested test?

The 2007 European Society of Hypertension and European Society of Cardiology (ESH/ESC) guidelines list an ankle-brachial index test as a recommended test for managing hypertension, with a result of <.9 an indicator of sub-clinical organ damage that affects prognosis.
The Heart Foundation's 'Guideline to Management of Hypertension 2008' recommends ankle-brachial index as a further investigation for patients with risk factors for Peripheral Arterial Disease ('PAD').