From the Guidelines
The Ankle Brachial Index (ABI) is a crucial diagnostic tool that deciphers the presence and severity of peripheral arterial disease (PAD) by comparing blood pressure in the ankle to blood pressure in the arm, with an ABI < 0.90 indicating PAD 1. The ABI test involves measuring systolic blood pressure in both arms and ankles using a blood pressure cuff and Doppler ultrasound device. The ABI is calculated by dividing the highest ankle pressure by the highest arm pressure. This simple, non-invasive test helps clinicians assess arterial blood flow to the legs, guide treatment decisions for PAD, evaluate cardiovascular risk, and monitor disease progression over time. Key points to consider when interpreting ABI results include:
- A normal ABI ranges from 0.9 to 1.4
- Values below 0.9 indicate PAD, with 0.7-0.9 suggesting mild disease, 0.4-0.69 moderate disease, and below 0.4 severe disease
- Values above 1.4 typically indicate non-compressible arteries due to calcification, often seen in diabetes or kidney disease PAD detection is crucial as it indicates systemic atherosclerosis and increased risk for heart attack and stroke, as supported by studies such as 1 and 1. According to the American Heart Association, an ABI < 0.90 should be considered the threshold for confirming the diagnosis of lower-extremity PAD 1. In cases where the ABI is >0.90 but there is clinical suspicion of PAD, postexercise ABI or other noninvasive tests may be used 1. Overall, the ABI is a valuable tool for diagnosing and managing PAD, and its use can help reduce morbidity and mortality associated with this condition.
From the Research
Ankle Brachial Index (ABI) Deciphering
The ankle brachial index (ABI) is a non-invasive test used to assess the presence and severity of peripheral arterial disease (PAD) in the lower limbs.
- The ABI test measures the ratio of blood pressure in the ankles to blood pressure in the arms, with a lower ratio indicating potential PAD 2.
- A systematic review of the diagnostic accuracy of ABI for PAD found that the test had high sensitivity (95-97%) and specificity (56-89%) in detecting significant arterial disease on angiography 2.
- Another study found that the ABI had low sensitivity (7-34%) and high specificity (96-100%) in a screening population, highlighting the need for further research on the test's diagnostic accuracy 3.
ABI and Cardiovascular Disease Risk Assessment
The ABI is also used to assess cardiovascular disease (CVD) risk, with studies suggesting that it can reclassify 10-year risk for coronary artery disease (CAD) 4.
- However, the addition of ABI to the Framingham Risk Score (FRS) probably has limited value for predicting CAD or CVD events 4.
- A systematic review found that treatment benefits for asymptomatic individuals with screen-detected PAD are not established, and that the current evidence is insufficient to assess the balance of benefits and harms of screening for PAD with the ABI in asymptomatic adults 5.
Association of ABI with Limb Revascularization or Amputation
Studies have found that ABI is associated with limb outcomes in patients with PAD, including revascularization and amputation 6.
- Patients with severe PAD (ABI <0.5) had a higher risk of revascularization, while those with poorly compressible arteries (ABI ≥1.4) had a higher risk of amputation 6.
- Guideline-recommended management strategies for secondary risk prevention are underused in community-dwelling patients with PAD, highlighting the need for improved management and treatment of the disease 6.