The ankle to brachial index can be used to evaluate a patient with peripheral artery disease involving the lower extremity. Measurements are relatively easy to take and the ratio is stable over time in the absence of disease progression.
Synonym: ankle pressure index
ankle to brachial index =
= (systolic blood pressure at the ankle in mm Hg) / (systolic blood pressure at the brachial artery in mm Hg)
Interpretation:
• The normal ratio is around 1.1. The systolic pressure in the ankle exceeds that in the arm because of pressure augmentation as the wave travels peripherally.
• A ratio >= 1 can rarely be seen in a patient with a significant arterial stenosis.
• A ratio <= 0.92 can rarely be seen in a patient without a significant arterial stenosis.
• A ratio < 0.50 suggests 2 or more levels of obstruction.
• A steady decline in values usually indicates worsening disease.
• An increased ratio may be seen after a successful revascularization or with development of collateral blood flow.
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