What does the Ankle-Brachial Index (ABI) measure?

The Ankle-Brachial Index (ABI) is a non-invasive test that specifically measures the ratio of blood pressure in the ankle compared to the blood pressure in the upper arm. This measurement is pivotal in assessing the presence of peripheral artery disease (PAD). By comparing these blood pressure readings, the ABI provides an indication of how well blood is flowing to the extremities. A lower ABI can suggest impaired blood flow due to narrowed arteries, which can help in diagnosing various cardiovascular conditions.

In contrast, the other options address different aspects of cardiovascular or vascular health without directly relating to the ABI's specific function. Blood pressure in both arms is measured to compare systemic blood pressure or to identify any significant difference that might suggest vascular issues; however, it doesn’t assess peripheral circulation as the ABI does. Measuring peripheral blood flow to the brain usually involves different criteria and techniques focused on cerebral blood flow rather than peripheral arteries. Assessing heart rate variability reflects autonomic nervous system function and does not provide information about blood flow in the limbs, making it unrelated to the ABI’s primary purpose.