What is the ankle-brachial index?
The ankle-brachial index (ABI) is a simple, noninvasive test for peripheral artery disease (PAD). It can be used to find out if you have PAD and to monitor you if you have PAD.
The ABI can show how severe PAD is, but it cannot identify the exact location of the blood vessels that are blocked or narrowed.
Peripheral artery disease
Peripheral artery disease causes poor blood flow to the legs and other parts of the body. This happens when the blood vessels are blocked or narrowed (arteriosclerosis).
Peripheral artery disease increases your risk of having a stroke, transient ischemic attack (TIA/mini-stroke), heart attack and other cardiovascular problems.
Symptoms of PAD can include pain or cramping in the legs or thighs when you exercise, and numbness or paleness of your legs and feet.
What are the advantages of the ABI test?
The ABI is the preferred way to diagnose PAD because it is simple, fast and sensitive. The test takes about 10 to 20 minutes and can be done in your doctor’s office or an outpatient clinic. The test does not cause any long-term problems.
Your doctor may want you to have an ABI test if you:
- Have a history of using tobacco.
- Have diabetes and are over age 50.
- Are over age 65.
- Have high cholesterol, high blood pressure, or a family history of heart disease.
You should not have the ABI test if you have excruciating leg pain, cut(s) on your legs or feet or deep vein thrombosis.
How is the ABI test done?
Before the test:
- DO NOT exercise during the hour before the test.
- DO NOT eat or drink anything that contains caffeine on the day of your test.
- DO wear loose-fitting, comfortable clothing.
You will lie down and rest for about 10 minutes before the test starts. During the test, the blood pressure in your arms (brachial artery pressures) are compared to the blood pressure in your ankles to find out how well your blood is flowing to your legs. The technician will also use an ultrasound to listen to your pulse.
What do the ABI test results mean?
The ABI itself is the systolic blood pressure reading (top number) in your ankle divided by the systolic blood pressure reading in your arm. If your ABI is 0.9 or lower, you should make an appointment with a vascular medicine specialist.
- An ABI ratio between 0 and 1.4 is normal.
- An ABI ratio between 0.9 and 1.0 is borderline.
- An ABI ratio of 0.9 or less means you have PAD.
- An ABI ratio between 0.4 and 0.7 means you have moderate PAD.
- An ABI ratio less than 0.4 means you have severe PAD.
- An ABI ratio higher than 1.4 could mean the blood vessels in your limbs are stiff due to advanced age or diabetes.
What type of follow-up do I need after an ABI test?
Your doctor will talk to you about the follow-up care you need after your ABI test. In general:
- You may need to have repeat ABI tests from time to time, especially if your ABI is outside of the normal range. Regular testing will help your doctor know if your PAD is getting worse. It can also be used to see how well treatments to open your blood vessels are working.
- You will need to schedule regular appointments with your doctor if you have PAD.
- Depending on your results, you may need other testing or treatments.
