BACKGROUND: Although numerous trials have demonstrated the diagnostic accuracy of coronary artery calcium (CAC) scanning for prediction of obstructive disease, virtually all studies have been performed using Electron Beam CT (EBCT). We evaluated the diagnostic accuracy of CAC by 64-row CT to detect obstructive coronary stenosis compared to quantitative coronary angiography (QCA) in the ACCURACY multicenter trial. METHODS: 16 sites prospectively enrolled 230 patients (pts) [59.5% males, 57yrs] with chest pain referred for invasive coronary angiography (ICA). Pts underwent CAC scan and CT angiography prior to ICA. Total CAC scores were correlated with angiographically documented stenoses using common cutpoints of CAC >0, >100 and >400. Significant obstructive disease was defined as >50% luminal stenosis by QCA. RESULTS: The per-patient accuracy of CAC by 64-row CT compared to QCA demonstrates a high sensitivity and low specificity for the presence of obstructive disease (>50% stenosis on QCA). With CAC >0, >100 and >400, the sensitivities to predict stenosis were 98%, 88%, and 60%, whereas the specificities were 42%, 71%, and 88%, respectively. CONCLUSIONS: Most previous CAC studies have focused on the fact that significant calcium places patients into a higher risk group in terms of future events, and should lead to more aggressive treatment with preventative therapies. This prospective multicenter results comparing 64-row CAC to QCA demonstrate that CAC using 64-row CT scanner, similar to previously published reports using EBCT, is highly sensitive and moderately specific test to predict significant coronary artery stenosis. The presence of abnormal levels of calcium may place patients into a higher risk group in terms of future events, and lead to more aggressive treatment with preventative therapies. However, the detection of calcium does not always help with a clinical diagnosis particularly in the presence of diffuse moderate coronary atheroma. Whether this information is complementary to CTA data remains to be validated.