ABI, also known as the Ankle-Brachial Index test, is a safe and painless test used to measure and compare the blood pressure in a patient’s ankles to the blood pressure in their arms. This test helps the physician gather useful information to determine if there is adequate blood supply to the patient’s legs.
When a patient’s circulatory system is healthy, the blood pressure taken in the brachial artery in the crook of the arm (which is near the heart) is a good indicator for the blood pressure in other areas in the body. When blood travels through stiff or cholesterol-clogged arteries, the pressure at areas further from the heart can be different from the pressure in the arms. This test compares the pressure in the arms to the pressure in the legs.
If the blood pressure at the ankle is the same or greater than the pressure recorded from the arm, it indicates no narrowing or blockage of blood flow. If the patient experiences a slight drop in the ABI after exercise it may indicate PAD. This is important because PAD is linked to a higher risk of stroke or heart attack.
It also lets the doctor see if there is any narrowing of the vessel that carries blood to the legs and to predict the severity of any peripheral arterial disease (PAD). The ABI test is also used to evaluate the effect of a previous medical treatment such as angioplasty, or surgery, or an exercise program.
The most common sign of PAD in the legs are pain or cramping in the calves, thighs, hips, or buttocks when exercising (including walking or climbing stairs) that goes away after rest. Wounds that don’t heal or take a long time to heal on the toes, feet; a leg that feels cooler than other parts of the body; or a leg that is a different color from the rest of your body are all signs of PAD and an indication of an ABI (Ankle-Brachial Index) test to be performed.
Often, PAD is asymptomatic until it reaches an advanced stage. People at high risk of developing the disease, such as smokers or former smokers over age 50; adults with diabetes, high blood pressure, or high cholesterol; those who have had a stroke or mini-stroke; and anyone with a strong family history of heart disease are recommended to have the ankle-brachial index test.
The ABI Test is done by measuring blood pressure at the ankle and in the arm while a person is at rest. After five minutes of walking on a treadmill, the blood pressure measurements are taken again.
No special preparations are needed prior to the test. Patients may eat and go about normal activities.
How is the ABI done?
- Patients are asked to undress from the waist down and put on a hospital gown or wear comfortable clothes.
- The patient is asked to lie on their back.
- The technician places blood pressure cuffs on the patient’s ankles and arms.
- The technician applies a small amount of jelly on the patient’s ankles and arms.
- The technician takes a scan using a transducer or probe.
- The blood pressure cuffs will inflate and recordings are taken of the patient’s ankles and arms.
- Sometimes the measurements are made before and after exercising.
The test will take about 20 minutes. The highest pressure recorded at the ankle is divided by the highest pressure recorded at the brachial artery. This gives the ankle-brachial index.