Coronary CT angiography (CCTA) is used as a triage test before invasive coronary angiography (ICA). In this study we assessed the level of agreement between the two methods in patients whose CCTA reported severe stenosis in the presence of a low coronary artery calcium (CAC) score. We retrospectively analyzed 124 patients selected from a total of 2,742 examinations who underwent both CCTA and ICA. A discordant group (n=33) had stenosis reported on CCTA together with a low CAC (<400 and <100 AU). Across the whole cohort, obstructive disease (≥50% in the left main coronary artery or ≥70% in the other segments) was present in 44.4% of patients. In the discordant subgroup, agreement between CCTA and ICA was markedly worse: ICA showed obstructive disease in only 6.1% of patients. These results suggest that, although CAC remains a stand-alone predictor of obstructive disease, its predictive value is limited in a population already selected by referral for catheterization. The substantial discrepancy observed in cases where CCTA reports severe disease in the presence of a low CAC score raises the possibility that CCTA overestimates stenosis severity. In patients showing this pattern of discordance, non-invasive functional testing before referral to ICA could therefore be useful.