September 28, 2013 in Features

Ankle-brachial test measures blood pressure

Anthony L. Komaroff M.D.
 

DEAR DOCTOR K: I had some pain in my leg while exercising, and now my doctor wants to do an ankle-brachial index test. How is it done? And what will it tell him?

DEAR READER: Atherosclerosis stiffens and clogs our arteries. It attacks the coronary arteries that provide blood to the heart muscle and causes heart attacks. It also attacks the arteries of the brain, causing strokes.

Atherosclerosis also often affects the peripheral arteries of the legs. When we exercise our leg muscles, they can reach the point where we’re asking them to work harder than their blood supply allows. When that happens, they scream in pain. Of course, many different conditions can cause leg pain when we exercise – injuries to leg muscles or to the hip, knee, ankle or foot can cause exercise pain.

A key test for problems in peripheral arteries is the ankle-brachial index, or ABI. An ABI compares blood pressure readings from the ankle and the brachial artery, which is the major blood vessel in the upper arm.

Normally, blood pressure is similar whether it is measured in the legs or in the arms.

The doctor will calculate your ABI by taking the highest pressure recorded at your ankle and dividing it by the highest pressure recorded at your arm. The normal range is between 0.90 and 1.30. A result under 0.90 means that blood is having a hard time getting to the legs and feet. The lower the number, the higher the chances of leg pain while exercising or of limb-threatening low blood flow.

On the other end, an ABI above 1.30 is usually a sign of stiff, calcium-encrusted arteries. These often occur in people with diabetes or chronic kidney disease.

The ABI also offers information about your general cardiovascular health. An ABI result under 0.90, for example, also indicates an increased risk of heart attack, stroke or dying of heart disease – people with severe atherosclerosis of the arteries of the leg usually also have atherosclerosis of the arteries of the heart and brain. I hope your test goes well and that the result is reassuring.

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