Ankle Brachial Index (ABI) Test
One of the most common ways to diagnose peripheral artery disease (PAD) and help measure vascular health is with an ankle-brachial index (ABI) test. During an ABI test, a vascular specialist first measures the blood flow in your arms and ankles. The blood pressure in your ankle is then divided by the blood pressure in your arm, determining your ankle-brachial index.
A low ankle-brachial index can indicate a blockage in an artery, preventing the proper nutrients from reaching the rest of your body. A low ABI test number also tells the doctor that your risk of circulatory issues has increased and that you should be monitored more regularly. This doesn’t mean your arteries are completely blocked, but there is evidence of narrowing, which must be treated in order to avoid future health conditions. Your legs need open arteries for blood to flow freely and deliver nutrients and oxygen to your limbs.
The procedure is quick and minimally invasive. If you suspect you need an ABI test, call USA Vascular Centers to schedule a visit.
Who Performs Ankle-Brachial Index Tests?
A trained healthcare provider can perform an ankle-brachial index test. Nurses, medical technicians, nurse practitioners, and doctors can all administer the test. However, only providers trained in vascular medicine can accurately interpret the ABI test results and give you information about any further tests you might need. At USA Vascular Centers, our team performs and analyzes the results of your ABI test.
Choosing a facility staffed with vascular specialists offers many benefits. If your ABI test results are outside the normal range, a vascular doctor can order or perform further testing. When an ABI test result shows signs of PAD, a quick and accurate diagnosis is key.
Should further testing be needed, the vascular specialists at USA Vascular Centers can perform angiograms to help make an accurate diagnosis. During an angiogram, a special dye (contrast agent) is injected into your vascular system. Usually, the vascular system cannot be visualized by X-ray, but the contrast agent makes it visible. This procedure can help confirm a PAD diagnosis and pinpoint the exact location of the blocked or narrowed arteries.
Once your vascular doctor knows more about how PAD is affecting you, he or she can put together a treatment plan to address the clogged arteries.
How is an Ankle Brachial Index Test Done?
On the day of your ABI test, you’ll want to avoid drinking caffeine or exercising about an hour beforehand. Wear loose-fitting, comfortable clothing that’s easy to relax in. Your doctor will have you lie on your back for 10 minutes before the test begins.
Using a handheld Doppler (a device that uses sound waves to estimate the speed of blood flow through your vascular system) and a blood pressure cuff, your doctor will calculate the systolic blood pressure in your upper arm. Your systolic blood pressure measures the force your heart applies to the walls of your arteries with every beat.
Your doctor will place the Doppler over the brachial artery and inflate and deflate the cuff, similar to a regular blood pressure test. They will then record the data and measure the waveforms of your blood pressure, as displayed on the Doppler screen. Your doctor will then take your pulse at various intervals, most likely between each reading.
This process will be repeated on your other arm, then on both ankles to measure the blood pressure and flow in the major arteries of the foot.
How Long Does an ABI Test Take?
An ankle-brachial index test takes about 15 to 20 minutes to complete, after which your vascular doctor will discuss the results with you. If your ABI test is within the normal range, your doctor can discuss the next steps with you. This might include another ABI test after a certain length of time to see if your condition has stayed the same.
If your ABI test is outside the normal range, your vascular doctor can recommend additional tests to help pin down a diagnosis. Your provider might also give you tips on managing any symptoms of PAD as you work toward getting treated for the condition.
Some providers might decide to do an exercise ABI test in addition to a resting ABI test. In this case, your provider will have you walk on a treadmill before the ABI test. This can help a vascular doctor get an idea of how well the blood flows in your vascular system during exercise. By performing an ankle-brachial index test after exercise, doctors can diagnose or rule out PAD as a cause of leg pain while walking (known as intermittent claudication). An exercise ABI test can take about 30 minutes to complete.
ABI Test Results
After measuring the systolic pressure in your arm and ankle, the doctor will divide the ankle value by the arm value. The resulting number is your ankle-brachial index. Here’s what the numbers mean:
- Above 1.4: Suggests calcification and hardening
- 1.0–1.4: Normal
- 0.9–1.0: Borderline
- 0.8–0.9: Some arterial disease
- 0.5–0.8: Moderate arterial disease
- Less than 0.5: Severe arterial disease
If your ankle-brachial index is above 1.4 or below 0.9, your doctor may recommend treatment. Numbers above 1.4 indicate that you may need a toe brachial index test (TBI) for a more accurate diagnosis.
How Accurate Is the Test?
Some estimates suggest that ABI tests have a 95% accuracy rate but can’t always definitively rule out or diagnose PAD. Let’s take a closer look at why this might be.
Studies have shown that a resting ankle-brachial index test has 68–84% sensitivity. In other words, it will accurately detect the presence of PAD in 68–84% of people who actually have PAD. On the other hand, a resting ABI test has an 84–99% specificity.
This means that it will accurately rule out PAD in 84–99% of people who don’t have it. In an exercise ankle-brachial index test, sensitivity increases by about 25%. That means that 25% more people who do have PAD will get an ABI test result that indicates the presence of narrowed arteries.
In short, ABI tests are reliable much of the time, but the accuracy of the test can vary based on factors such as a person’s health history and whether a resting or exercise ABI test was done. If you have any questions or concerns about the accuracy of ABI tests, talk to your doctor. At USA Vascular Centers, our highly skilled vascular specialists are dedicated to accurately diagnosing PAD through ABI tests and angiograms.
Next Steps After Ankle Brachial Index Test
Depending on your ABI test results, your vascular specialist may guide you toward making important lifestyle changes, such as modifying your diet, starting an exercise routine, or quitting smoking. They may also prescribe medication to help lower your blood pressure or cholesterol, prevent blood clots from developing, or help manage diabetes.
An angioplasty may be needed to help determine whether any arteries are narrowed, signaling atherosclerosis due to plaque buildup, a major symptom of PAD.
If you have PAD, your doctor may recommend a minimally invasive treatment to help ease the symptoms. Our specialists at USA Vascular Centers offer minimally invasive procedures to help treat peripheral artery disease, including:
- Angioplasty, a treatment that involves inserting a balloon-tipped catheter into your blood vessels, then inflating the balloon to open narrowed arteries.
- Stent placement, wherein your specialist places a mesh stent inside the narrowed blood vessel to help it stay open.
- Atherectomy, a procedure in which your doctor removes the plaque in affected blood vessels.
Schedule an Appointment with USA Vascular Centers
If you wish to get an ABI test or have already received results from a test and need to speak with a vascular specialist, the trusted experts at USA Vascular Centers can help. Schedule a consultation with one of our vascular specialists online or call us at 888-773-2193 today.
Medically Reviewed by:
Dr. Aaron Shiloh, M.D., FSIR
Dr. Aaron Shiloh is a board-certified interventional radiologist with decades of experience performing minimally invasive treatment for PAD and other vascular conditions. Dr. Shiloh was awarded a fellowship from the Society of Interventional Radiology, a prestigious distinction that only the top 10% of doctors in his field have earned.