The ankle-brachial index is one of the most useful tests for finding out whether the arteries in the legs are carrying blood properly. It is inexpensive, quick and painless, and it is often the first step in diagnosing poor circulation before it causes serious problems.
What the ankle-brachial index is
The ankle-brachial index (ABI) is the result of dividing the blood pressure measured at the ankle by the pressure measured at the arm. If the arteries in the leg are narrowed, the pressure at the ankle drops, and so does the index. This number therefore gives a simple picture of how well blood is reaching the leg.
How it is done
It is very similar to taking your blood pressure. You lie down for a few minutes and a cuff is placed on the arm and another on the ankle. A small ultrasound device (Doppler) detects the pulse and measures the pressure at each point. The ratio is then calculated. The whole process takes just a few minutes and causes no discomfort.
How to read the result
The value obtained falls within general reference ranges. The final interpretation is always made by the doctor together with your symptoms:
| ABI value | General interpretation |
|---|---|
| Above 1.3 | Stiff or calcified arteries (non-compressible); the result is not reliable. |
| 1.0 – 1.3 | Normal. |
| 0.9 – 1.0 | Borderline normal. |
| Below 0.9 | Suggests peripheral arterial disease. |
| Below 0.4 | Severe obstruction; blood flow seriously compromised. |
An index below 0.9 supports a diagnosis of poor arterial circulation, even if there are no symptoms yet. The lower the number, the more significant the obstruction tends to be.
It's a five-minute test that can get ahead of a serious problem by years. In patients with diabetes or a history of smoking, doing it in time can make all the difference.
What it is used for and when it is requested
The ankle-brachial index is used to detect and measure peripheral arterial disease, assess its severity and monitor its progress. It is usually indicated when there is leg pain when walking, wounds that will not heal, weak pulses in the foot, cardiovascular risk factors, or diagnostic uncertainty.
What happens next
If the index is low, the next step is to precisely locate the obstruction using Doppler ultrasound and, if treatment is being considered, imaging tests such as CT angiography or arteriography. All of this guides the approach: from controlling risk factors to restoring blood flow. You can see the options on the peripheral arterial disease page.
In summary
The ankle-brachial index is a simple test that says a lot: with a single number it indicates whether your arteries are carrying blood well to your legs. It is especially valuable for catching the problem early in people at risk. If you have symptoms or risk factors, ask your specialist for a vascular assessment that includes this measurement.