Ankle-Brachial Index (ABI) & Segmental Studies

Peripheral Arterial Disease Diagnosis

These are noninvasive tests to detect peripheral arterial disease (PAD), which causes problems with blood flow to the legs. ABI is a measurement of the blood pressure at the ankle compared with a blood pressure measurement in the arm. It is expressed as a ratio (ABI = ankle pressure ÷ arm pressure).

Normally, the ankle pressure should be the same as or slightly higher than the arm pressure, meaning the ABI = 1. If the ABI is less than 1, then there is likely to be artery disease present. An ABI of less than 0.6 indicates severe PAD, and an ABI less than 0.3 indicates critical blood flow impairment, which may warrant surgery.

Toe-Brachial Index

In some patients, we may also do a toe-brachial index (TBI), using a cuff on the big toe. A segmental pressure test involves placing a series of blood pressure cuffs on the legs (high thigh, low thigh, high calf, and ankle) to help determine where in the leg the artery disease might be. For instance, a significant pressure drop across the high thigh and low thigh cuffs in a leg might indicate a narrowing or blockage in the femoral artery, which travels through the thigh from the groin to the knee.

If You Are Scheduled for an ABI Test

These tests are performed at MarinHealth Vascular Medicine in Greenbrae and Novato. There are no special instructions prior to the test. We want you to be relaxed and wearing comfortable clothing. Please arrive approximately 15 minutes prior to the procedure to register. You should take all of your regular medications, and you do not need to fast. The test is performed by a registered vascular technician (RVT).

For the test, you will need to remove pants because we will need access to your entire leg. Loose fitting shorts or a skirt is acceptable. You will lay flat for the study, and you will feel some pressure in your legs momentarily as the cuffs inflate. The study takes approximately 20 minutes. The exam findings will be sent to your physician. You will be notified immediately if there are any critical exam findings.