Which ankle-brachial index (ABI) value is most indicative of a patient experiencing pain in the feet at night?

The ankle-brachial index (ABI) is a useful diagnostic tool in evaluating peripheral arterial disease (PAD) and can indicate the severity of vascular obstruction. A normal ABI value is typically in the range of 1.0 to 1.4, which indicates healthy blood flow. As the ABI value decreases, it signifies a greater degree of arterial insufficiency.

An ABI value of 0.4 or lower indicates severely reduced blood flow to the limbs, which is often associated with critical limb ischemia. Patients with such low ABI values may experience severe limitations in walking, resting pain, and pain in the feet at night. This is due to the significantly impaired perfusion, making it difficult for the tissues to receive adequate oxygen and nutrients, especially during times of rest when blood flow is naturally reduced.

In contrast, higher ABI values, such as 1.0 and 0.8, suggest more normal or slightly compromised perfusion, which would not typically result in nocturnal foot pain. An ABI of 0.6 depicts more moderate insufficiency but is not at the critical level that typically causes nighttime pain. Thus, an ABI value of 0.4 is most indicative of severe ischemia, directly correlating with the patient's experience