Ankle Brachial Index (ABI) test – Doppler required

Definition:
The Ankle Brachial Index (ABI) is the ratio of the blood pressure in the ankle (distal leg) compared to the blood pressure measured in the arm. In order to obtain a ABI value by divide the systolic blood pressure at the ankle by the systolic blood pressure in the arm.

Test procedure:
To obtain an accurate ABI index, a Doppler wand and sphygmomanometer are required.
Firstly, the highest systolic reading between the left and right arm brachial artery is noted.

Secondly, the systolic reading of the left and right posterior tibial artery are measured with the Doppler wand. Then the left and right dorsalis pedis artery is measured in similar fashion.
Use the highest value (systolic) recorded in the lower limbs in the calculation of the ABI.

Test findings:
A healthy result will indicate a higher systolic value in the ankle/leg when compared to the arm.

A lower blood pressure in the distal legs compared to the arm may be indicative of peripheral vascular diseases such as arteriosclerosis.
With the ABP index calculated a score between;
• 0.9 and 1.2 is considered normal,
• ABI index lower than 0.9 indicates arterial disease.
• An ABP index value greater than 1.3 suggests calcification of the arteries and vasculature, with potential severe Peripheral Arterial Disease (PAD).

Special considerations:
When performed by specialists the ABP index is an accurate and non-invasive method of assessing PAD and vascular health. Whereas in primary care settings false positives are high and the test may be considered unreliable in this setting.