Ankle-brachial index

Definition

The ankle-brachial index allows health professionals to determine if healthy circulation is occurring in the patient's legs. Blood pressure measurements are taken at the ankle and the arm and then compared.

Purpose

The ankle-brachial index is designed to help doctors determine whether blood flow is to a patient's legs is adequate. It is generally used to test for peripheral artery disease. According to the American Heart Association, about 8 million Americans have peripheral artery disease. It occurs when the arteries in the legs become hardened and narrowed. This limits the amount of blood getting to the tissues and muscles of the legs. This can lead to wounds that do not heal, skin ulcers, and even gangrene . It can also lead to an increased likelihood of heart attack and stroke . The ankle-brachial index helps determine if peripheral artery disease exists, and if does, the severity of the disease.

Precautions

The exercise component sometimes performed for the ankle-brachial test may not be appropriate for individuals with extreme cardiovascular heath problems. Individuals with kidney disease or who have had diabetes for many years may not be good candidates for this test. These individuals often have rigid blood vessels that make a correct blood pressure reading difficult or impossible to obtain using standard equipment. Seniors are also more likely to have rigid blood vessels, as blood vessels can become more rigid with advanced age. Therefore the test may not be appropriate for all seniors.

Description

During the ankle-brachial index test the patient is usually asked to lie flat. Blood pressure measurements are then taken on the arm and the ankle. In some cases measurements are taken on each arm to ensure accurate results. These blood pressure readings are then compared. For healthy individuals, the blood pressure readings in the ankle and arm should be about the same.

In some cases only an at-rest ankle-brachial index measurement is taken. In other cases, however, it is repeated after mild exercise. The individual is asked to walk on a treadmill for five minutes. The individual is ten asked to lie down again, and the blood pressure measurements are repeated.

QUESTIONS TO ASK YOUR DOCTOR

• If the test shows that I have peripheral artery disease, what is the next step?
• How can I prevent peripheral artery disease?
• When should I have another ankle-brachial index test?

KEY TERMS

Brachial —Of the arm or relating to the arm.

Preparation

No preparation is required for testing the ankle-brachial index.

Aftercare

No aftercare is required.

Complications

No complications are expected in most individuals. Individuals with peripheral artery disease may experience pain in the legs during the exercise portion of the test.

Results

The results of the ankle-brachial index indicate whether peripheral artery disease exists and if so, the extent of the disease. They are:

• 0.95 to 1.2: Normal circulation to the legs.
• 0.8 to 0.95: Possible mild peripheral artery disease. Some hardening or narrowing of the blood vessels in the legs have occurred. Symptoms are not generally present or noticeable.
• 0.4 to 0.8: Moderate peripheral artery disease. Significant hardening or narrowing of one or many blood vessels of the leg have occurred. Symptoms may occur as pain in the affected area during exercise.
• 0.25 to 0.4: Severe peripheral artery disease. Extreme hardening or narrowing of the blood vessels of the legs have occurred.
• Below 0.25: Severe peripheral artery disease likely to present. A real and immediate danger to the limbs. Hardening and narrowing of the blood veins so sever significant blood flow is cut off to the affected area.

An ankle blood pressure reading after walking on the treadmill that is the same or slightly higher than the at-rest blood pressure indicates healthy circulation. If the ankle pressure is lower after walking on the treadmill it is an indication of peripheral artery disease.

Caregiver concerns

A doctor determines the need for an ankle-brachial index measurement to be taken. He or she will explain the test, why it is recommended, and the meaning of the possible results to the patient. A nurse will take the blood pressure readings and report the results to the doctor and to the patient. The doctor then determines what, if any, further course of action is appropriate.

Resources

BOOKS

Fortmann, Stephen P. and Prudence E. Breitrose. The Blood Pressure Book: How to Get it Down and Keep it Down. Boulder, CO: Bull Pub. Co., 2006.

White, William B., ed. Blood Pressure Monitoring in Cardiovascular Medicine and Therapeutics, 2nd Ed. Totowa, NJ: Humana Press, 2007.

PERIODICALS

Kirner, Katherine. “When to Use the Ankle-Brachial Index: Controversy Persists Over the ABI Test and How to Read its Results. The Author Sorts Through the Evidence to Arrive at Some Recommendations.” Clinical Advisor 10.8 (August 2007): 49-53.

Splete, Heidi. “Ankle-Brachial Index Can Help Identify Arterial Leg Ulcers.” Internal Medicine News 40.4 (Feb 15, 2007): 24-25.

Zoler, Mitchel L. “Exercise Ankle-Brachial Index Boosts PAD Diagnosis.” Family Practice News 35.23 (Dec 1, 2005): 17-18.

ORGANIZATIONS

Vascular Disease Foundation, 1075 S. Yukon, Suite 320, Lakewood, CO, 80226, 866-723-4636, http://www.vdf.org/.

Robert Bockstiegel