What is the Ankle Brachial Index (ABI)?

From the Guidelines

The ankle-brachial index (ABI) is a crucial diagnostic tool for peripheral artery disease (PAD), with a normal range of 0.9 to 1.4, and values below 0.9 or above 1.4 indicating potential disease or calcified arteries, respectively, as stated in the 2017 ESC guidelines 1.

Key Points to Consider

• The ABI test is simple, non-invasive, and compares blood pressure measured at the ankle with blood pressure measured at the arm to evaluate blood flow to the legs.
• Values below 0.9 suggest PAD, with lower numbers indicating more severe disease: mild PAD (0.7-0.9), moderate (0.4-0.69), and severe (<0.4) 1.
• Values above 1.4 may indicate calcified, non-compressible arteries, and alternative tests such as toe pressure or toe-brachial index (TBI) may be necessary 1.
• The test should be performed after the patient has been resting for 5-10 minutes in a supine position, and the highest systolic pressure from each ankle is divided by the highest arm pressure.
• ABI is particularly useful for diagnosing PAD in patients with risk factors such as smoking, diabetes, hypertension, or hyperlipidemia, especially those with leg pain, non-healing wounds, or diminished pulses 2.

Diagnostic Recommendations

• The resting ABI should be used to establish the lower extremity PAD diagnosis in patients with suspected lower extremity PAD, defined as individuals with exertional leg symptoms, nonhealing wounds, age 65 years and older, or 50 years and older with a history of smoking or diabetes 2.
• 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 2.
• ABI results should be uniformly reported with noncompressible values defined as greater than 1.40, normal values 1.00 to 1.40, borderline 0.91 to 0.99, and abnormal 0.90 or less 2.

From the Research

Ankle Brachial Index Overview

• The ankle-brachial index (ABI) is a screening method for the diagnosis of lower extremity peripheral arterial disease (PAD) 3.
• ABI is also recognized as a prognostic marker of adverse cardiovascular events due to its relation to atherosclerosis in other vascular territories 3.
• The ABI value can be influenced by different physiological characteristics, including age, sex, body position, and techniques used for ABI determination 3.

Diagnostic Accuracy of ABI

• The diagnostic accuracy of ABI for the diagnosis of PAD in people with leg pain on exercise that is alleviated by rest is sparse 4.
• A single study included in a systematic review provided limb-level data from a few participants, showing sensitivity of 97% and specificity of 89% for oscillometric ABI, and sensitivity of 95% and specificity of 56% for doppler ABI 4.
• The ABI threshold was not reported in the study, and the superiority of the oscillometric method over the manual method with a doppler probe used by inexperienced operators may be a clinically important finding 4.

ABI for Cardiovascular Disease Prediction

• Adding the ABI to the Framingham Risk Score (FRS) probably has limited value for predicting coronary artery disease (CAD) or cardiovascular disease (CVD) 5.
• The magnitude of the net reclassification improvement (NRI) was probably small when the ABI was added to the FRS to predict CAD or CVD events 5.
• Treatment benefits for asymptomatic individuals with screen-detected PAD are not established, and evidence on treatment benefits and harms is limited to aspirin and is scant 5, 6.

Screening for Peripheral Artery Disease with ABI

• There is no direct evidence and limited indirect evidence on the benefits of PAD screening with the ABI in unselected or asymptomatic populations 6, 7.
• Available studies suggest low sensitivity and lack of beneficial effect on health outcomes, but these studies have important limitations 6.
• The US Preventive Services Task Force (USPSTF) concludes that the current evidence is insufficient to assess the balance of benefits and harms of screening for PAD and CVD risk with the ABI in asymptomatic adults 7.