Objective To evaluate the prevalence and characteristics of coronary atherosclerosis in asymptomatic subjects classified as low risk by National Cholesterol Education Program (NCEP) guideline using coronary CT angiography (CCTA).

Design An observational study.

Setting A single tertiary referral centre.

Patients 2133 (49.2%) subjects, who were classified as low risk by the NCEP guideline, of 4339 consecutive middle-aged asymptomatic subjects who underwent CCTA with 64-slice scanners as part of a general health evaluation.

Main outcome measures The incidence of atherosclerosis plaques, significant stenosis.

Results In the subjects at low risk, 11.4% (243 of 2133) of subjects had atherosclerosis plaques, 1.3% (28 of 2133) of subjects had significant stenosis, and 0.8% (18 of 2133) of subjects had significant stenosis caused by non-calcified plaque (NCP). Especially, 75.0% (21 of 28) of subjects with significant stenosis and 94.4% (17 of 18) of subjects with significant stenosis caused by NCP were young adults. Mid-term follow-up (29.3±14.9 months) revealed four subjects with cardiac events: three subjects with unstable angina requiring hospital stay and one subject with percutaneous coronary intervention.

Conclusions Although an asymptomatic population classified as low risk by the NCEP guideline has been regarded as a minimal risk group, the prevalence of atherosclerosis plaques and significant stenosis were not negligible. However, considering very low event rate for those patients, CCTA should not be performed in low-risk asymptomatic subjects, although CCTA might have the potential for identification of high-risk groups in the selected subjects regarded as a minimal-risk group by NCEP guideline.