Ankle-Brachial Index (ABI)

What is an ankle-brachial index?

The ankle-brachial index (ABI) is an easy, non-invasive test for peripheral artery disease (PAD). Once you know you have PAD, you can repeat the test to see how you’re doing after treatment.

The ABI can tell your healthcare provider:

• How severe your PAD is, but it can’t identify the exact location of the blood vessels that are blocked or narrowed.
• If your arms and legs are getting enough oxygen.
• How bad your vascular injury is after a trauma.
• Your risk of dying from a cardiovascular issue. Even if you aren’t having symptoms, having PAD is a sign of a higher risk of death from a cardiovascular cause.

Catching PAD early gives people a chance to make lifestyle changes and get treatment that may reduce their risk of cardiovascular issues.

What is peripheral artery disease (PAD)?

Peripheral artery disease is a condition that causes poor blood flow to your legs and other parts of your body. This happens when your blood vessels are blocked or narrowed from atherosclerosis.

Peripheral artery disease increases your risk of:

• Stroke.
• Transient ischemic attack (TIA/mini-stroke).
• Heart attack.
• Other cardiovascular problems.

What are the advantages of the ankle-brachial index test?

The ankle-brachial index test is the preferred way to screen at-risk people and diagnose PAD because it’s:

• Simple.
• It takes about 10 to 20 minutes.
• Low-cost.
• It can be done in your provider’s office or an outpatient clinic.
• It’s noninvasive and doesn’t cause any long-term problems.

When would an ankle-brachial index be needed?

Your doctor may want you to have an ankle-brachial index test if you:

• Have a history of using tobacco products.
• Have diabetes and are older than age 50.
• Are older than age 65.
• Have high cholesterol, high blood pressure or a family history of heart disease.

You should not have the ankle-brachial index test if you have:

• Severe leg pain.
• Cut(s) on your legs or feet.
• Deep vein thrombosis.

Who performs an ankle-brachial index test?

Nurses usually perform an ankle-brachial index test. However, doctors, nurse practitioners and other healthcare providers can give the test. People often get the test in a primary care provider’s office. However, you may get the test while you’re in the hospital.

How is the ankle-brachial index test done?

Your healthcare provider will check the blood pressure of specific arteries in your arms and your ankles.

They’ll use an ultrasound device (sound waves) to listen to the blood flow in the arteries they’re using to check your blood pressure.

How do I prepare for an ankle-brachial index test?

Before your test:

• Don’t exercise during the hour before the test.
• Don’t eat or drink anything that contains caffeine on the day of your test.
• Don’t use tobacco products or alcohol for one hour before your test.
• Wear loose-fitting, comfortable clothing.
• Tell your healthcare provider if you’ve had any procedures to improve circulation in your legs.
• Go to the restroom and pee until your bladder is empty.

What to expect on the date of the test

You’ll lie down and rest for about 10 to 30 minutes before the test starts. You should keep lying on your back during the test.

Because your arms and ankles need to be at heart level during blood pressure measurement, they may be propped up on pillows or cushions.

Your provider may use an ultrasound device to listen to your pulse and blood flow before taking each of your blood pressure readings. This helps them find the best artery to use for the test.

What to expect during an ankle-brachial index test

Your healthcare provider will:

1. Check the blood pressure of the brachial artery in one of your arms.
2. Check the blood pressure in your dorsalis pedis or posterior tibial artery in your ankle area on the same side as the arm they just measured.
3. Check the blood pressure in the ankle of your other leg.
4. Check the blood pressure in your other arm.
5. Calculate your ankle-brachial index by dividing your higher systolic (top number) ankle blood pressure by your higher systolic arm blood pressure.

What to expect after an ankle-brachial index test

This is a noninvasive test that doesn’t require anesthesia or skin punctures. After the test, you can go back to doing everything you normally do.

What are the risks of an ankle-brachial index test? Are there side effects?

Although you might feel some discomfort when the blood pressure cuffs tighten, side effects are rare.

What type of results do you get and what do the results mean?

After your healthcare provider takes your blood pressure and makes the ankle-brachial index calculation, you’ll get a number that ranges from less than 1 to a little higher than 1.

A normal ankle-brachial index is between 1.0 and 1.4.

How is ankle-brachial index calculated?

To calculate the ankle-brachial index, take the higher of your two systolic (top number) blood pressures from your two ankle arteries and divide that by the higher systolic blood pressure from your two arm readings. Some people use an average of each pair of readings instead of the higher number.

What does a low ankle-brachial index mean?

If your ABI is 0.9 or lower, you have PAD. You should make an appointment with a vascular medicine specialist. A low ankle-brachial index means you have a higher risk of:

• Heart attack.
• Kidney disease.
• High blood pressure.
• Stroke.

If you have PAD symptoms, but your ABI is just a little low, your provider may want to check your ABI again after you walk on a treadmill. An abnormal result is a decrease of 20% or more after you exercise.

What does a high ankle-brachial index mean?

An ABI ratio higher than 1.4 could mean the blood vessels in your limbs are stiff because of advanced age or diabetes. Researchers have found that people with an ankle-brachial index higher than 1.4 had twice the risk of cardiovascular death.

When should I know the results of my ankle-brachial index test?

The healthcare provider performing your ankle-brachial index test may be able to share results with you when they finish the test. If not, follow up with the provider who ordered the test.

When should I call my doctor?

Contact your healthcare provider if you didn’t get results right after your ankle-brachial index test. Depending on your results, you may need to schedule other testing or treatments.

If you have PAD, you‘ll need to schedule regular appointments with your provider.

You may need to repeat the ankle-brachial index test from time to time, especially if your number is outside of the normal range. Regular testing will help your provider know if your PAD is getting worse. It can also tell your provider how well treatments to open your blood vessels are working.

A note from Cleveland Clinic

Having an ankle-brachial index test is a quick and easy way to know if you have peripheral artery disease (PAD). There’s nothing to fear with this test, which doesn’t involve any needles, cuts or sedatives. If your healthcare provider determines that you have the disease, you’ll be doing yourself a favor by catching it early. Treatments are available to improve your condition.