If you’re a healthy person without any circulatory issues, blood flows to and from your extremities, like your legs and feet, without any problems.

But in some people, the arteries begin to narrow, which may impede the flow of blood to some parts of your body. That’s where a noninvasive test called an ankle brachial index test comes in.

An ankle brachial index test is a quick way for your doctor to check the blood flow to your extremities. By checking your blood pressure in different areas of your body, your doctor will be better prepared to determine whether or not you have a condition called peripheral artery disease (PAD).

In this article, we’ll take a closer look at what an ankle brachial index test is, how it’s done, and what the readings may mean.

In essence, an ankle brachial index (ABI) test measures the blood flow to your legs and feet. The measurements can highlight any potential problems, like blockages or partial blockages in blood flow to your extremities.

The ABI test is particularly useful because it’s noninvasive and easy to conduct.

If you have PAD, your limbs may not be getting enough blood. You may feel symptoms like pain or muscle cramps when you’re walking, or possibly numbness, weakness, or a coldness in your legs.

What distinguishes PAD from other causes of leg pain are the symptoms that arise after a defined distance (e.g. 2 blocks) or time (e.g. 10 minutes of walking) and are relieved by rest.

Left untreated, PAD can lead to painful symptoms and it may increase your risk of losing a limb.

Not everyone needs an ABI test. But people with certain risk factors for peripheral artery disease can possibly benefit from one. Typical risk factors for PAD include:

Your doctor might also recommend an ankle brachial index test if you’ve been experiencing leg pain when walking, which can be a symptom of PAD. Another possible reason to get a test is if you’ve undergone surgery on the blood vessels of your legs, so your doctor can monitor the blood flow to your legs.

Additionally, a 2017 study found benefits in conducting a post-exercise ABI test on people who had suspected PAD but normal test results while at rest.

According to the U.S. Preventive Services Task Force, the potential benefit in using the test in people without PAD symptoms hasn’t been very well studied.

The good news about this test: It’s fairly quick and painless. Plus, you don’t have to do any special preparations before getting the test.

Here’s how it works. You lie down for a few minutes before the test begins. A technician will take your blood pressure in both arms and in both ankles, using an inflatable cuff and a handheld ultrasound device to hear your pulse.

The technician will start by putting a blood pressure cuff on one arm, usually the right arm. They will then rub a little gel on your arm right above your brachial pulse, which is just above the inside crease of your elbow. As the blood pressure cuff inflates and then deflates, the tech will use the ultrasound device or Doppler probe to listen for your pulse and record the measurement. This process is then repeated on your left arm.

Next come your ankles. The process is very similar to the one performed on your arms. You will remain in the same reclined position. The tech will inflate and deflate a blood pressure cuff around one ankle while using the ultrasound device to listen for your pulse in the arteries that supply blood to your foot. The process will then be repeated on the other ankle.

After the technician has completed all the measurements, those numbers will be used to calculate the ankle brachial index for each leg.

The measurements from the ABI test are converted into a ratio. For example, the ABI for your right leg would be the highest systolic blood pressure in your right foot divided by the highest systolic pressure in both arms.

Experts consider a normal range for an ABI test result to fall between 0.9 and 1.4.

Your doctor may be concerned if your ratio is below 0.9. This index is what one 2014 study called “a powerful independent marker of cardiovascular risk.” This puts you at risk of developing progressively shorter walking distances (lifestyle limiting claudication).

In advanced stages, PAD progresses to chronic limb threatening ischemia (CLTI) in which patients have rest pain (continual, burning pain) from lack of blood flow and/or develop non healing wounds. CLTI patients have a dramatically higher rate of amputation compared to patients with intermittent claudication.

Finally, while PAD does not cause heart disease or cerebrovascular disease, patients with PAD typically have atherosclerotic disease in other blood vessels. Thus, having PAD is associated with an increased risk for non-limb major adverse cardiac events such as stroke or heart attack.

Your doctor will also want to take into account any possible signs of peripheral vascular disease that you may be experiencing before making a diagnosis.

Your family history and smoking history, as well as an examination of your legs for signs like numbness, weakness, or a lack of pulse, will need to be considered, too, before a diagnosis is made.

An ankle brachial index test, also known as an ABI test, is a quick and easy way to get a read on the blood flow to your extremities. It is a test that your doctor can order if they are concerned you may have symptoms of peripheral artery disease, or that you may be at risk for this condition.

This test can be very useful as one component of making a diagnosis of a condition like peripheral artery disease. This can help ensure that you get the most appropriate treatment right away.