Ankle brachial index and intima media thickness predict cardiovascular events similarly and increased prediction when combined

Objective: To compare the predictive value of the ankle brachial index (ABI) and carotid intima media thickness (IMT) for cardiovascular events.

Study Design and Setting: Population-based cohort study. New cardiovascular events (myocardial infarction [MI], stroke, angina, and intermittent claudication) were ascertained over a 12-year period in 1,007 men and women aged 60-79 and free of MI or stroke.

Results: The positive and negative predictive values for an ABI <= 0.9, an IMT >= 0.9 mm and for both tests abnormal were not substantially different. However, event rates in subjects with one test normal were increased when the alternate test proved positive (in people with a normal ABI test, 20.8% with an abnormal IMT developed MI/stroke compared with only 10.3% with a normal IMT). The area under the receiver operator curves (AUC) increased significantly between a model containing only age and sex (AUC 0.60, 95% confidence interval [CI] 0.55, 0.65) and that with either ABI (AUC 0.63, 95% CI 0.58, 0.69, P = 0.002) or IMT (AUC 0.62, 95% CI 0.57, 0.67, P = 0.005) added. The AUC increased further when both tests were added simultaneously (AUC 0.65, 95% CI 0.60, 0.70, P < 0.001).

Conclusion: The ability of the ABI to predict cardiovascular disease was similar to that of the IMT. Combination of the two tests may be advantageous when the second test is applied to people with a negative first test and/or when the results are used as continuous variables.