Ankle Brachial Index Test

What is an ankle brachial index test?

The ankle brachial index, or ABI, is a simple test that compares the blood pressure in the upper and lower limbs. Health care providers calculate ABI by dividing the blood pressure in an artery of the ankle by the blood pressure in an artery of the arm. The result is the ABI. If this ratio is less than 0.9, it may mean that a person has peripheral artery disease (PAD) in the blood vessels in his or her legs.

In PAD, plaque builds up in the arteries. It often affects the vessels that bring blood to the legs. The reduced blood flow can cause pain and numbness. Low ABI may mean that your legs and feet aren’t getting as much blood as they need. An ABI test won’t show exactly which blood vessels have become narrowed or blocked, though.

During an ankle brachial index test, you lie on your back. A technician takes your blood pressure in both of your arms using an inflatable cuff, similar to the one used in the doctor’s office. The technician also measures the blood pressure in the ankles. The doctor uses these values to compute your ABI.



Why might I need an ankle brachial index test?

Your doctor might want you to have an ankle brachial index test if you are at risk for PAD. Things that can increase your risk include:

  • Smoking
  • Diabetes
  • Age greater than 70
  • Elevated levels of lipids in the blood
  • Known plaque formation in other arteries, like the coronary arteries in your heart

Your doctor also might recommend an ABI if you have symptoms of PAD, like pain in the legs with activity. Not everyone with PAD has symptoms, though, which makes the test even more important.

You also might need an ABI to check the severity of your PAD. Your doctor might order this test every year, to see if your condition is getting worse.

If you’ve had surgery on the blood vessels of your legs, your doctor might want an ABI to see how well blood is flowing into the leg. Sometimes doctors use ABI to gauge your risk of future heart attack or stroke.

What are the risks for an ankle brachial index test?

For most people, there are no risks associated with having an ABI test. This test is not recommended if you have a blood clot in your leg. You might need a different type of test if you have severe pain in your legs.

How do I prepare for an ankle brachial index test?

There is very little you need to do to prepare for an ABI test. You can follow a normal diet on the day of the test. You shouldn’t need to stop taking any medications before the procedure.

You may want to wear loose, comfortable clothes. This will allow the technician to easily place the blood pressure cuff on your arm and ankle. You’ll need to rest for at least 15 to 30 minutes before the procedure. Ask if your doctor has any special instructions.

What happens during an ankle brachial index test?

The test is very similar to a standard blood pressure test. Ask your doctor about what you can expect. In general, during your ABI test:

  • You will lie flat during the procedure.
  • A technician will place a blood pressure cuff just above your ankle.
  • The technician will place an ultrasound probe over the artery. He or she will use this to listen to the blood flow through the vessel.
  • The technician will inflate the blood pressure cuff. He or she will increase the pressure until the blood stops flowing through the vessel. This may be a little uncomfortable, but it won’t hurt.
  • The technician will gradually release the pressure in the cuff. The systolic pressure is the pressure at which the blood flow is heard again. That is the part of the blood pressure measurement needed for the ABI.
  • The technician will repeat this process on your other ankle and on both of your arms.
  • Next, the technician will calculate the ABI. The numerator is the higher systolic blood pressure found in the ankles. The denominator is the higher systolic blood pressure found in the arms.

Sometimes, health care providers will combine an ABI test with an exercise test. You might have an ABI done before and right after exercise, to see how exercise changes this value.

What happens after an ankle brachial index test?

You should be able to go back to your normal activities right after your ABI test.

Be sure to follow up with your doctor about your results. In some cases, you may need follow-up testing to get more information about a blocked vessel. This might include a magnetic resonance angiogram (MRI) or an arteriogram.

If you have PAD, you may need treatment. Possible treatments include:

  • Stopping smoking
  • Treating high blood pressure, high cholesterol, and diabetes, if necessary
  • Staying physically active
  • Eating a healthy diet
  • Taking medication to increase blood flow to the legs or to prevent blood clots
  • Having procedures to restore blood flow, like angioplasty
  • Having surgery to the leg (if the blockage is severe)

Talk to your doctor about what your ABI value means for you.

Next steps

Before you agree to the test or the procedure make sure you know:

  • The name of the test or procedure
  • The reason you are having the test or procedure
  • The risks and benefits of the test or procedure
  • When and where you are to have the test or procedure and who will do it
  • When and how will you get the results
  • How much will you have to pay for the test or procedure