Espinola-Klein C et al. (2008) Different calculations of ankle–brachial index and their impact on cardiovascular risk prediction. Circulation 118: 961–967

Peripheral artery disease is a good predictor of cardiovascular events. Ankle–brachial index (ABI) is a simple, noninvasive screening tool that can be used to identify both symptomatic and asymptomatic, lower-extremity peripheral artery disease; an ABI value of <0.9 indicates the presence of disease. Current guidelines suggest ABI should be measured as the ratio of the highest systolic blood pressure (BP) of the two ankle arteries to the highest systolic BP of the arms; however, many published studies suggest that the use of the average, or even the lowest, systolic BP measurements might improve risk prediction.

Espinola-Klein and colleagues assessed patients admitted to hospital with chest pain to determine whether ABI underestimates the risk of cardiovascular events when the highest BP values are used for calculation. Follow-up information was collected for 812 patients for a median of 6.6 years. Patients who had an ABI <0.9 calculated using the highest BP measurements had increased mortality, but not an increased rate of total cardiovascular events, compared with patients who had an ABI ≥0.9 with the highest measurements but <0.9 when calculated using the lowest BP measurements. Patients with ABI ≥0.9 regardless of which BP measurements were used had the best event-free survival.

The authors conclude that clinicians should use the lowest (rather than the highest) ankle and arm systolic BP measurements in their ABI calculations to increase the reliability of cardiovascular risk prediction.