Ankle-brachial index

Ankle-Brachial Index (ABI) is a simple, non-invasive diagnostic tool used in medicine to detect peripheral arterial disease (PAD). The ABI is calculated by dividing the systolic blood pressure at the ankle by the systolic blood pressure in the arm.

Overview

The Ankle-Brachial Index is a measure of the drop in blood pressure in the arteries supplying the lower limbs. It is a useful indicator of atherosclerosis, which can lead to peripheral arterial disease (PAD). PAD is a condition where the arteries in the legs, or less commonly the arms, are narrowed or blocked. This can lead to pain and discomfort, particularly when walking, and in severe cases can result in limb amputation.

Procedure

The ABI is calculated by taking the highest systolic blood pressure from either the dorsalis pedis or posterior tibial arteries (found in the ankle) and dividing it by the highest systolic blood pressure from either the left or right brachial artery (found in the arm). The procedure is performed using a handheld Doppler device or an automatic blood pressure measuring device.

Interpretation

An ABI of 1.0 to 1.4 is considered normal. An ABI of less than 0.9 indicates PAD. An ABI of less than 0.4 indicates severe PAD. An ABI of more than 1.4 may suggest calcified, non-compressible arteries.

Limitations

The ABI has some limitations. It may not be accurate in patients with significant calcification of the arteries, such as those with diabetes or renal disease. In these patients, the arteries may be non-compressible, leading to an overestimation of the ABI.

See Also

• Peripheral arterial disease
• Atherosclerosis
• Doppler ultrasound

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