Ankle-Brachial Index (ABI)

The Ankle-Brachial Index (ABI) is a non-invasive diagnostic test performed to determine the severity of peripheral artery disease (PAD), a condition of narrowing or blocking of the arteries in your legs or arms. PAD also increases the risk of stroke and heart attacks. The ankle-brachial index is determined by comparing the blood pressures of the ankle and the arm. A low ABI value indicates narrowing of the peripheral arteries.

Indications

The ABI test is indicated to determine the severity of PAD. It may also be recommended to check the efficacy of prescribed therapy (medicines, exercise, angioplasty or surgery) for PAD.

Procedure

Ankle-brachial index test is performed at the doctor’s office and doesn’t require any specific preparation. You will have to lie on the table; your doctor will use a standard blood pressure cuff to measure the pressure in your arms and also in the arteries at the ankle. A hand-held ultrasound device may be pressed on your skin to hear the pulse. The ankle-brachial index is calculated by dividing the highest blood pressure at the ankle by the highest blood pressure at the arms. The test is sometimes performed at rest and after exercise.

Results

The normal value of ABI test at rest is 1.0 to 1.2 and it indicates absence of narrowed or blocked peripheral arteries. The range of ABI values indicates the condition of arteries as below:

• ABI of 0.5 to 0.9 indicates narrowing or blocked arteries which can result in pain while exercising
• ABI of less than 0.4 indicates severe PAD or Critical Limb Ischaemia
• ABI of more than 1.2 indicates stiff arteries

If you are diabetic or have chronic kidney disease, the ABI test measured by standard procedure may not be accurate due to calcification (hardening) of the arteries.  In such patients, measuring blood pressure at the less rigid arteries of the toe may provide more accurate results.