Definition

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.

Why it’s done

Ask your doctor if you should have this test if you are age 50 or older and have any of these risk factors for peripheral artery disease:

• Smoking
• Diabetes
• Overweight (a body mass index of 25 or greater)
• High blood pressure
• High cholesterol

Risks

The test may not adequately measure the ankle-brachial index if you have severe diabetes or calcified arteries with significant blockage. Instead, your doctor may need to read your blood pressure at your big toe to get an accurate index number if you have either of these conditions.

How you prepare

Generally, you won’t need to follow any special instructions before your appointment to have an ankle-brachial index test performed.

What you can expect

You lie on a table on your back, and your doctor measures your blood pressure in both your arms using an inflatable cuff. Then, your doctor measures the blood pressure in two positions in your left ankle using the inflatable cuff and a hand-held Doppler device that your doctor will press on your skin. The Doppler device lets your doctor hear your pulse in your ankle arteries after the cuff is deflated.

The procedure for performing an ankle-brachial index test may vary slightly, based on your doctor’s preference.

Having an ankle-brachial index test is painless and similar to getting your blood pressure taken in a routine visit to your doctor. You may feel some pressure on your arm or ankle when the cuff inflates to read your blood pressure.

Results

When the ankle-brachial index test is complete, your doctor calculates your ankle-brachial index by dividing the higher of the two blood pressure measurements at your arms by the higher of the two blood pressure measurements at the arteries near your ankle. Based on the number your doctor calculates, your ankle-brachial index may indicate:

• 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.