The Ankle Brachial Index Test is an essential component used for risk stratification for PAD. The ABI is used to screen for hemodynamically significant disease and to help define its severity. With the patient in the supine position, bilateral brachial blood pressures are obtained. A blood pressure cuff is placed on the calf of each leg, and an ankle systolic pressure is obtained. Determining ankle systolic pressure may require the use of Doppler US. The ABI is calculated by dividing the ankle systolic pressure by the highest systolic pressure from either arm.
Ankle-Brachial Index Test (ABI) – Why am I having this test?
Ankle-brachial index test is used to diagnose peripheral vascular disease (PVD). PVD is also known as peripheral arterial disease (PAD). PVD is the blocking or hardening of the arteries anywhere within the circulatory system beyond the heart. PVD is caused by:
- Cholesterol deposits in your blood vessels (atherosclerosis). This is the most common cause of this condition.
- Irritation and swelling (inflammation) in the blood vessels.
- Blood clots in the vessels.
Cholesterol deposits cause arteries to narrow. Normal delivery of oxygen to your tissues is affected, causing muscle pain and fatigue. This is called claudication.
PVD means that there may also be a buildup of cholesterol:
- In your heart. This increases the risk of heart attacks.
- In your brain. This increases the risk of strokes.
What is being tested?
The ankle-brachial index test measures the blood flow in your arms and legs. The blood flow will show if blood vessels in your legs have been narrowed by cholesterol deposits.
How do I prepare for this test?
- Wear loose clothing.
- Do notuse any tobacco products, including cigarettes, chewing tobacco, or e-cigarettes, for at least 30 minutes before the test.
What happens during the test?
- You will lie down in a resting position.
- Your health care provider will use a blood pressure machine and a small ultrasound device (Doppler) to measure the systolic pressures on your upper arms and ankles. Systolic pressure is the pressure inside your arteries when your heart pumps.
- Systolic pressure measurements will be taken several times, and at several points, on both the ankle and the arm.
- Your health care provider will divide the highest systolic pressure of the ankle by the highest systolic pressure of the arm. The result is the ankle-brachial pressure ratio, or ABI.
Sometimes this test will be repeated after you have exercised on a treadmill for 5 minutes. You may have leg pain during the exercise portion of the test if you suffer from PVD. If the index number drops after exercise, this may show that PVD is present.
How are the results reported?
Your test results will be reported as a value that shows the ratio of your ankle pressure to your arm pressure (ABI ratio). Your health care provider will compare your results to normal ranges that were established after testing a large group of people (reference ranges). Reference ranges may vary among labs and hospitals. For this test, a common reference range is:
- ABI ratio of 0.9 to 1.3.
How is the ABI interpreted?
A normal ABI is slightly greater than 1. A significant obstruction to blood flow to the lower extremities reduces the ankle pressure and the ABI. The risk of PAD and other cardiovascular disease as well as symptoms increases as the ABI decreases
Ankle-Brachial Index (ABI) by Symptoms
| ABI | SYMPTOMS |
|---|---|
| 1-1.10 | Normal |
| 0.3-0.9 | Claudication |
| ≦0.5 | Rest pain |
| ≦0.2 | Tissue loss |
Ankle-Brachial Index (ABI) by Cardiovascular Risk
| ABI | CARDIOVASCULAR RISK CATEGORY |
|---|---|
| >1.40 | Noncompressible arteries (increased risk) |
| 1.00-1.40 | Normal (no/low risk) |
| 0.91-0.99 | Borderline (probably normal; no/low risk) |
| 0.70-0.89 | Abnormal (low/moderate risk) |
| 0.50-0.69 | Abnormal (moderate/high risk) |
| <0.49 | Abnormal (high risk) |
What do the results mean?
An ABI ratio that is below the reference range is considered abnormal and may indicate PVD in the legs.
What can cause a falsely elevated ABI?
The ability to determine the systolic blood pressure accurately is predicated by the ability to compress the artery and obstruct blood flow. Diabetes mellitus may cause significant calcification of peripheral vessels, making them difficult to compress; this would elevate the observed cuff pressure and the calculated ABI and could create false-negative tests.
Talk with your health care provider about what your results mean.
Questions to ask your health care provider
Ask your health care provider, or the department that is doing the test:
- When will my results be ready?
- How will I get my results?
- What are my treatment options?
- What other tests do I need?
- What are my next steps?
Summary
- The ankle-brachial index (ABI) test is used to diagnose peripheral vascular disease (PVD). PVD is also known as peripheral arterial disease (PAD).
- The ankle-brachial index test measures the blood flow in your arms and legs.
- The highest systolic pressure of the ankle is divided by the highest systolic pressure of the arm. The result is the ABI ratio.
- An ABI ratio that is below 0.9 is considered abnormal and may indicate PVD in the legs.
