From the Guidelines
The normal Ankle-Brachial Index (ABI) starts at 1.0, not 0.9. An ABI of 1.0-1.4 is considered within the normal range, indicating healthy arterial blood flow to the lower extremities. Values between 0.9-0.99 are considered borderline and may suggest mild peripheral artery disease (PAD) 1. An ABI below 0.9 is diagnostic of PAD, with lower values indicating more severe disease: moderate PAD (0.6-0.89), severe PAD (0.4-0.59), and critical limb ischemia (<0.4). The ABI is calculated by dividing the highest systolic blood pressure at the ankle by the highest systolic blood pressure in the arm. This measurement is valuable because it reflects the ratio of blood pressure in the lower extremities compared to the upper extremities, providing insight into arterial circulation and potential blockages in the legs.
Key Points
- An ABI of 1.0-1.4 is considered normal 1
- Values between 0.9-0.99 are considered borderline and may suggest mild PAD 1
- An ABI below 0.9 is diagnostic of PAD 1
- The ABI is a useful tool for diagnosing and monitoring PAD, with a sensitivity of 68%–84% and a specificity of 84%–99% 1
Calculation of ABI
The ABI is calculated by dividing the highest systolic blood pressure at the ankle by the highest systolic blood pressure in the arm. This measurement is valuable because it reflects the ratio of blood pressure in the lower extremities compared to the upper extremities, providing insight into arterial circulation and potential blockages in the legs 1.
Interpretation of ABI Results
The results of the ABI test can be interpreted as follows:
From the Research
Ankle-Brachial Index (ABI) Values
- Normal ABI values typically range from 0.9 to 1.4, with values below 0.9 indicating potential peripheral arterial disease (PAD) 2, 3, 4, 5, 6
- An ABI value of 0.9 is often used as a cutoff point to identify patients with PAD, with sensitivity and specificity of 75% and 86%, respectively 2
- However, some studies suggest that ABI values between 0.9 and 1.0 may be considered borderline, and values between 1.0 and 1.09 may be considered low normal 4
Diagnostic Value of ABI
- ABI is a useful tool for identifying patients with PAD, with a pooled diagnostic odds ratio of 15.33 and a summary receiver operator curve area under the curve of 0.87 2
- ABI values can also predict cardiovascular risk and are associated with higher SYNTAX scores, more myocardium at risk, and less complete coronary revascularization 5, 6
Clinical Implications
- ABI values should be interpreted in the context of clinical symptoms and other diagnostic tests, as correlations between ABI and symptomatology can be weak 3
- ABI values can be influenced by various physiological characteristics, including age, sex, body position, and techniques used for ABI determination 5