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?
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.
The leg pain caused by atherosclerosis is usually felt in the calf, though sometimes it is felt in the thigh. Typically, the pain starts only after a person has been exercising his or her legs for a while. That’s when the muscles suddenly are being asked to work harder than they can, because of their reduced blood supply. When a person stops exercising, pain caused by atherosclerosis typically goes away over the next minute or two.
Of course, many different conditions can cause leg pain when we exercise. In particular, injuries to leg muscles or to the hip, knee, ankle or foot can cause exercise pain. Just from your symptoms alone, it can be hard to be sure what is causing leg pain when you exercise.
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. The test is done using a blood pressure cuff and an ultrasound probe.
Normally, blood pressure is similar whether it is measured in the legs or in the arms. If blood pressure is lower in the legs, it usually means that fatty buildup inside the leg arteries is interfering with circulation.
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. That’s because 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.