An ABI of less than 0.4 is associated with which condition?

An Ankle-Brachial Index (ABI) of less than 0.4 is indicative of severe peripheral arterial disease, which can lead to critical limb ischemia. In this context, ischemia refers to a condition where the blood flow to a part of the body is insufficient to meet the metabolic needs of tissues, often due to significant blockage in the blood vessels.

When the ABI value drops below 0.4, it signals severe obstruction in the arteries. This level of obstruction typically means that the arterial supply is critically reduced, resulting in inadequate blood flow which can cause pain at rest, non-healing ulcers, or even tissue necrosis. The ABI serves as a crucial non-invasive test in assessing the severity of arterial insufficiency and determining risk for limb loss.

In contrast, normal blood flow would present with an ABI typically between 0.9 and 1.3, while calcified vessels, often seen in patients with diabetes or chronic renal failure, can lead to falsely elevated ABI levels, complicating the interpretation and masking true ischemic conditions. Therefore, a low ABI unmistakably reflects severe ischemic changes in limb perfusion.