What Is an Ankle-Brachial Index Test?
An ankle-brachial index (ABI) test is a simple way for your doctor to check how well your blood is flowing in your legs.
Doctors use this test to check for peripheral artery disease (PAD). When you have this condition, it means you have blockages in the arteries of your arms and legs. This slows your blood flow, so your limbs don’t get all the oxygen they need.
The ABI test compares the blood pressure at your ankle with the blood pressure at your arm. If you have a low score on this test, you probably have poor blood flow in your legs.
Why Might You Need an Ankle-Brachial Index Test?
You may need the ankle-brachial index test because you already have a PAD diagnosis and your doctor wants to check its progression. Or you might have symptoms of PAD like:
- Pain when you climb stairs
- Heavy, numb, or weak legs when you exert yourself
- Less hair on your legs than normal
- One leg feels colder
- Skin looks pale or kind of blue
- Sores on your toes, feet, and legs that don’t heal the way they should
- Toenails that grow more slowly than they once did
- Trouble getting an erection, often in men who have diabetes
At checkups, your doctor will typically ask about your family and personal health history. Just being over 50 raises your risk for PAD. Other risk factors include:
Your doctor may suggest the test if you have a number of these risk factors or show other signs of PAD.
What Happens During an Ankle-Brachial Test?
The test takes 10 to 15 minutes. First, you lie down on a table. Your doctor wraps a cuff around your arm to take your blood pressure. You’ll feel mild pressure while it inflates, but that doesn’t last long.
Your doctor will use a Doppler ultrasound device, a plastic tool that’s a little smaller than a computer mouse. It connects to a speaker so they can hear your blood flow.
To use the device, your doctor will first put a dab of gel on your arm just below the blood pressure cuff. Then, they’ll put the ultrasound device on the gel. This helps them know when to take your blood pressure reading.
They’ll do the same steps on your other arm and then on both ankles.
If you have leg pain and your doctor wants to make sure it’s PAD, you might take an exercise ankle-brachial index test. For this, you’ll have two ankle-brachial index readings: one before and one after walking on a treadmill.
How Do You Interpret Ankle-Brachial Test Results?
Your doctor uses the blood pressure results to come up with a number called an ankle-brachial index, which is a ratio of the ankle to brachial systolic BP. Here’s what the numbers mean:
- 0.9 or less. You have PAD. The lower the number, the more blockage you have in your arteries.
- 0.91-0.99. This result is acceptable but might mean that you have borderline PAD.
- 1.0-1.4. You don’t have PAD.
- Over 1.4. Numbers this high mean you have stiff arteries and you can’t get useful blood pressure numbers with the cuff. Because of this, the test isn’t helpful for you. Your doctor will turn to a different test.
If you took an exercise ankle-brachial index test, the range of results may be a little different.
Your doctor will look at your results, symptoms, and health history to help you decide what comes next. You may need to change your lifestyle or start taking medicine. In some cases, your doctor may say you need surgery.
If you have severe PAD, your doctor may send you to a vascular specialist, a doctor who treats diseases in arteries and veins.
Are There Risks for the Ankle-Brachial Test?
This test doesn’t usually have much risk. Your doctor will probably use a different test if you have a blood clot in your leg or if you have serious leg pain.