What are the ankle brachial index (ABI) criteria for diagnosing and managing peripheral artery disease (PAD)?

From the Guidelines

The Ankle Brachial Index (ABI) criteria for diagnosing and managing peripheral artery disease (PAD) are based on a normal range of 1.0-1.4, with an ABI <0.9 confirming PAD diagnosis, values between 0.91-0.99 considered borderline, and an ABI >1.4 suggesting non-compressible vessels due to arterial calcification. The ABI is a key diagnostic tool for PAD, with specific criteria for interpretation.

• A normal ABI ranges from 1.0-1.4
• An ABI <0.9 confirms PAD diagnosis
• Values between 0.91-0.99 are considered borderline, suggesting possible early disease
• Severe PAD is indicated by an ABI <0.5
• Critical limb ischemia is typically associated with values <0.4
• An ABI >1.4 suggests non-compressible vessels due to arterial calcification, particularly common in diabetic patients, requiring alternative testing 1. For diagnosis, systolic blood pressure is measured in both arms and at the dorsalis pedis and posterior tibial arteries of both ankles, with the higher ankle pressure divided by the higher brachial pressure to calculate the ABI.
• In patients with symptoms but normal resting ABI, exercise ABI testing should be performed, with a post-exercise decrease in ABI >20% supporting PAD diagnosis
• ABI measurements should be performed in patients with risk factors for PAD (smoking, diabetes, hypertension, hyperlipidemia), those over 65, or patients with exertional leg symptoms or non-healing wounds
• The ABI guides management decisions, with lower values indicating more severe disease requiring more aggressive treatment approaches including antiplatelet therapy, statins, risk factor modification, and possibly revascularization for severe cases 1. It is essential to consider the clinical context and patient population when interpreting ABI results, as the sensitivity and specificity of the test may vary depending on the presence of risk factors and disease prevalence 1. The most recent guidelines recommend using the ABI as a first-line noninvasive test for screening and diagnosis of PAD, with a threshold value of 0.9 for detecting significant stenosis 1. However, it is crucial to note that the ABI should not be considered a binary marker for the diagnosis of PAD, and values between 0.91 and 1.00 should be considered borderline, requiring further evaluation and clinical judgment 1.

From the Research

Ankle Brachial Index Criteria

The ankle brachial index (ABI) is a diagnostic test used to identify peripheral artery disease (PAD). The criteria for diagnosing PAD using ABI are as follows:

• An ABI value of ≤ 0.90 is considered abnormal and indicative of PAD 2, 3, 4, 5
• The sensitivity and specificity of ABI ≤ 0.90 for diagnosing PAD vary across studies, with sensitivity ranging from 15-89% and specificity ranging from 83-99% 2
• The diagnostic accuracy of ABI ≤ 0.90 for PAD is high, with a pooled diagnostic odds ratio of 15.33 and a summary receiver operator curve area under the curve of 0.87 5

Measurement of Ankle Brachial Index

The measurement of ABI is crucial for accurate diagnosis of PAD. The following points should be considered:

• ABI should be measured in both the posterior and anterior tibial arteries to ensure accurate diagnosis 6
• The use of low ankle pressure (LAP) method, which considers the lower of the two ankle arterial systolic blood pressures, may increase the diagnostic yield of ABI 3, 4
• The high ankle pressure (HAP) method, which considers the higher of the two ankle arterial systolic blood pressures, may have lower sensitivity but higher specificity compared to the LAP method 3, 4

Clinical Implications

The ABI criteria have significant clinical implications for the diagnosis and management of PAD:

• An ABI value of ≤ 0.90 can be used as a simple and useful tool to identify PAD with serious stenosis in clinical practice 2, 5
• The use of ABI can help identify patients with PAD who are at increased risk of cardiovascular events and mortality 6
• ABI can be used as a non-invasive test to diagnose PAD, reducing the need for more invasive tests such as angiography 2, 3, 4