From the Guidelines
The normal Ankle-Brachial Index (ABI) in legs ranges from 0.9 to 1.31, as indicated by the most recent and highest quality study 1. This measurement is obtained by dividing the systolic blood pressure at the ankle by the systolic blood pressure in the arm. An ABI value within this range indicates healthy arterial circulation in the lower extremities. Values below 0.9 suggest peripheral arterial disease (PAD), with severity increasing as the number decreases:
- mild PAD (0.7-0.9)
- moderate PAD (0.4-0.69)
- severe PAD (<0.4). Conversely, an ABI above 1.4 may indicate calcified, non-compressible arteries, often seen in patients with diabetes or end-stage renal disease. The ABI is a simple, non-invasive diagnostic tool that provides valuable information about arterial blood flow to the legs. It works by comparing blood pressure in the legs to that in the arms, as atherosclerotic disease typically affects the legs before the arms, making this ratio an effective indicator of vascular health, as supported by previous studies 1.
Some key points to consider when interpreting ABI results include:
- The ABI should be measured in both legs in all new patients with PAD of any severity to confirm the diagnosis of lower extremity PAD and establish a baseline 1.
- The toe-brachial index should be used to establish the lower extremity PAD diagnosis in patients in whom lower extremity PAD is clinically suspected but in whom the ABI test is not reliable due to noncompressible vessels (usually patients with long-standing diabetes or advanced age) 1.
- Leg segmental pressure measurements are useful to establish the lower extremity PAD diagnosis when anatomic localization of lower extremity PAD is required to create a therapeutic plan 1.
Overall, the ABI is a valuable tool for diagnosing and managing PAD, and its results should be interpreted in the context of the patient's overall clinical presentation and medical history, as recommended by the most recent guidelines 1.
From the Research
Ankle-Brachial Index (ABI) Values
- A normal Ankle-Brachial Index (ABI) is typically considered to be between 0.9 and 1.4 2, 3, 4, 5, 6
- An ABI value less than 0.9 is generally considered abnormal and may indicate peripheral arterial disease (PAD) 2, 3, 4, 6
- An ABI value greater than 1.4 may indicate arterial stiffness and calcification 5