More recently, large multi-center studies have been reported using fast CT for diagnosis of obstructive CAD in symptomatic persons (n = 1851), who underwent coronary angiography for clinical indications. Study prediction models were designed to be continuous, adjusted for age and sex, corrected for verification bias, and independently validated in terms of their incremental diagnostic accuracy. The overall sensitivity was 95%, and specificity was 66% for coronary calcium score to predict obstructive disease on invasive angiography. The logistic regression model exhibited excellent discrimination (receiver operating characteristic curve area of 0.84 ± 0.02) and calibration (chi-square goodness of fit of 8.95, p = 0.44) (38). Increasing the cut-point for calcification markedly improved the specificity, but decreased the sensitivity. In the same study, increasing the CAC cutpoint to greater than 80 decreased the sensitivity to 79% while increasing the specificity to 72%. In another large study (n = 1764) comparing CAC to angiographic coronary obstructive disease, use of a CAC score greater than 100 resulted in a sensitivity of 95% and a specificity of 79% for the detection of significant obstructive disease by angiography (39). Summing these 2 large studies (n = 3615) leads to an estimated sensitivity of 85%, with a specificity of 75%. There is some concern, due to study design, that these studies (similar to validation of many non-invasive cardiovascular tests) are subject to verification bias, which could raise the sensitivity and lower the specificity. A large study, evaluating consecutive symptomatic persons undergoing cardiac catheterization, addresses this concern. 2115 consecutive symptomatic patients (n = 1404 men; mean age = 62, SD ± 19 years old) with no prior diagnosis of CAD were included in this study. These patients were being referred to the cardiac catheterization laboratory for diagnosis of possible obstructive coronary artery disease, without knowledge of the CAC scan results. The scan result did not influence the decision to perform angiography. Overall sensitivity was 99%, and specificity was 28% for the presence of any coronary calcium being predictive of obstructive angiographic disease. With volume calcium score greater than 100, the sensitivity to predict significant stenoses on angiography decreased to 87% and the specificity increased to 79% (40).