Level 1: Likely reliable evidence
A prospective cohort study evaluated 2,600 participants aged 50 years and older who had colon cancer screening with multidetector CT colonography and same-day colonoscopy (N Engl J Med. 2008;359:1207-1217). Analysis included 2,531 participants (97%) with complete colonographic and colonoscopic results. The reference standard was colonoscopy with histologic confirmation. Prevalence of lesions >10 mm was 5.2% and 5-9 mm was 10.2%.

For adenoma or carcinoma >10 mm, per-patient predictive performance of CT colonography had 90% sensitivity, 86% specificity, 23% positive predictive value, and 99% negative predictive value. For adenoma or carcinoma >6 mm, per-patient predictive performance of CT colonography had 78% sensitivity, 88% specificity, 40% positive predictive value, and 98% negative predictive value.

Current limitations of CT colonography include serious adverse events (0.24%), lower sensitivity for smaller polyps, colonoscopy required to follow up a positive result, and the unknown effects of cumulative radiation dose if repeated every five years.

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These results are consistent with those from a previously published cohort study involving 1,233 asymptomatic adults (mean age 58 years) who had same-day virtual and conventional colonoscopy (N Engl J Med. 2003;349:2191-2200).