Ankle Brachial Index (ABI)

What is the Ankle-Brachial Index?

The ankle-brachial index, or ABI, is a simple painless test. It compares the blood pressure measured at your ankle with the blood pressure measured at your arm. In a healthy circulation the two pressures are close to equal. When arteries in the legs are narrowed by plaque, pressure at the ankle drops. The ratio between the two numbers then falls below normal. That is why the ABI is the standard first test for peripheral artery disease, often shortened to PAD. In that condition, the arteries carrying blood to the legs become narrowed. The test uses ordinary blood pressure cuffs and a small handheld Doppler ultrasound probe. The probe listens to the pulse. Nothing is injected, no radiation is used, and no needles are involved. The test is done in the office in roughly 15 to 30 minutes. Dr. Vimal Nanavati can review the numbers with you the same day.

Why Dr. Nanavati may recommend this

Peripheral artery disease is common, often silent, and an important marker of risk elsewhere in the body. Someone with narrowed leg arteries frequently has narrowing in the heart and neck arteries too. The American Heart Association describes peripheral artery disease and its symptoms, and MedlinePlus offers a plain language overview.

Screening for PAD is part of our broader cardiology services. Dr. Nanavati may recommend an ABI if you have:

• Cramping, aching, or heaviness in the calf, thigh, or buttock that starts with walking and eases with rest, a symptom called claudication.
• Leg pain at rest, especially at night, or pain that improves when you dangle your leg over the bed.
• A sore, ulcer, or wound on the foot or toes that is slow to heal.
• Cold feet, weak or absent foot pulses, hair loss over the shins, or shiny skin on the legs.
• Diabetes, kidney disease, high blood pressure, or a history of smoking.
• Known coronary artery disease or narrowing found on a carotid ultrasound.
• A need to check how well treatment for PAD is working over time.

How to prepare

Very little preparation is needed, and you can eat normally.

• Wear loose clothing, or pants that can be rolled above the knee. You may be asked to change into shorts or a gown.
• Skip knee-high compression stockings on the day of the test.
• Avoid nicotine and caffeine for a few hours beforehand. Both temporarily tighten blood vessels and can shift the reading.
• Take your regular medications, including blood pressure pills, unless told otherwise. Bring your list so the results can be read in context.
• Tell the office if you have a wound, graft, or recent surgery on an arm or leg. Mention a mastectomy with lymph node removal too, since a cuff may need to be placed differently.
• Plan to rest quietly for about 10 minutes before the measurements begin. Walking in from the parking lot right before the test can lower the numbers.
• Allow about 30 minutes, or up to an hour if exercise testing is added.

What happens during the procedure

You lie flat on your back on an exam table, with your head and heels supported. You rest quietly for several minutes so your blood pressure settles.

Blood pressure cuffs are placed on both upper arms and both ankles. A small amount of clear gel goes over the pulse points. A handheld Doppler probe is then held gently against the skin. The probe turns blood flow into an audible whooshing sound. That sound tells the technician exactly when flow returns as the cuff deflates.

Each cuff is inflated briefly and then released. You feel the familiar squeeze of a blood pressure cuff and nothing more. Several readings are taken at each site, including two different arteries at each ankle.

The highest ankle pressure on each side is divided by the higher of the two arm pressures. That ratio is your ABI, calculated separately for the right and left leg.

Sometimes the test is repeated after walking on a treadmill for a few minutes. Exercise can unmask a narrowing that looks normal at rest. If your arteries are stiff and hard to compress, a toe pressure may be measured instead.

Recovery and results

There is no recovery. The gel is wiped off and you get dressed. You can drive, work, and exercise immediately.

Results are available right away, because the calculation is simple arithmetic. In general, a resting ABI between about 1.0 and 1.4 is normal, 0.91 to 0.99 is borderline, and 0.90 or lower supports a diagnosis of peripheral artery disease. Lower numbers suggest more severe narrowing. A value above 1.4 usually means the arteries are calcified and too stiff to compress. That pattern is common in diabetes and kidney disease, and it calls for a toe-brachial index instead.

Dr. Nanavati interprets the number alongside your symptoms and examination. Mild disease is usually managed with a structured walking program and smoking cessation. Cholesterol and blood pressure control and diabetes care matter just as much. More significant findings may lead to an arterial Doppler ultrasound to map the narrowing. Occasionally they lead to a catheter-based procedure.

Risks and safety

The ABI is one of the safest tests available. There are no needles, no dye, no radiation, and no medication.

The only real discomfort is the pressure of the cuff. Some people find it briefly uncomfortable, particularly at the ankle. Tell the technician if you have a painful leg ulcer, fragile skin, or a recent bypass graft. The cuff can then be placed carefully, or the test modified.

If exercise testing is added, walking may bring on the leg cramping you already experience. The treadmill is stopped as soon as you ask, and the discomfort resolves with rest.

The main limitation is accuracy rather than safety. Stiff calcified arteries can produce a falsely normal or falsely high value. So a normal ABI does not always rule out disease when symptoms are convincing. In that situation additional imaging is used rather than relying on the number alone.

Related services and conditions

• Arterial Doppler ultrasound to locate and grade a narrowing.
• Carotid ultrasound and Doppler for the neck arteries.
• Coronary artery disease, which often coexists with PAD.
• Advanced lipid testing for a fuller risk picture.
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