What is the role of the ankle-brachial index (ABI) in the evaluation of peripheral arterial occlusive disease (PAOD)?

Updated: Sep 12, 2019
  • Author: Josefina A Dominguez, MD; Chief Editor: Vincent Lopez Rowe, MD  more...
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Answer

A useful tool in assessing a patient with claudication is the ankle-brachial index (ABI), which is calculated as the ratio of systolic blood pressure at the ankle to systolic blood pressure in the arm. The ABI can help quantify the presence and severity of disease. A normal ABI is 0.9-1.1. By definition, any patient with an ABI lower than 0.9 has some degree of PAOD. As PAOD worsens, the ABI decreases further.

A 2011 study investigated whether subjects not considered to be at high risk for cardiovascular disease had abnormal ABIs. [6] Cardiovascular risk was determined on the basis of the Framingham Risk Score: 56.3% of the study subjects were at low risk for cardiovascular disease, 25.8% at intermediate risk, and 17.9% at high risk. Only a relatively low percentage (~12%) of participants had a low or intermediate Framingham Risk Score while still having an abnormal ABI. This study demonstrated the close association of cardiovascular disease with PAOD.

The ABI may be a less accurate assessment tool in patients with diabetes who have PAOD. Peripheral vessels in patients with diabetes may have extensive medial-layer calcinosis, which renders the vessel resistant to compression by the pneumatic cuff. These patients should be referred to a vascular laboratory for further evaluation. In this situation, the use of the toe-brachial index (TBI) may be helpful.


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