Colorectal cancer in patients with single versus double positive faecal immunochemical test results: A retrospective cohort study from a public tertiary hospital

BACKGROUND: Screening for colorectal cancer (CRC) using the faecal immunochemical test (FIT) is widely advocated. Few studies have compared the rate of detecting colonoscopic pathologies in single compared to double FIT-positive follow-up colonoscopy-compliant individuals in a two-sample national FIT screening program. OBJECTIVE: To compare CRC incidence in double FIT-positive versus single FIT-positive individuals using a retrospective cohort of patients from a tertiary hospital in Singapore. DESIGN: Retrospective cohort study. SETTING: Data was extracted from one public tertiary hospital in Singapore. PARTICIPANTS: 1,422 FIT-positive individuals from the national FIT screening program who were referred to the hospital from 1st January 2017 to 31st March 2020 for follow-up consultation and diagnostic colonoscopy. MEASUREMENTS: The exposure of interest was a positive result on both FIT kits. The main outcome was a follow-up diagnostic colonoscopy finding of CRC. The secondary outcome was a diagnostic colonoscopy finding of a colorectal polyp. RESULTS: Incidence density of CRC was 1.15 and 13.10 per 100,000 person-months, in the single and double FIT-positive group, respectively. This resulted in an incidence rate ratio of 11.40 (95% CI = 4.34, 35.09). Colorectal polyp detection was significantly higher (p < 0.01) in the double (103 of 173 participants; 59.5%) compared to the single (279 of 671 participants; 41.6%) FIT-positive group. LIMITATIONS: The key limitation of this study was the relatively small cohort derived from a single tertiary hospital, as this had the effect of limiting the number of incident cases, resulting in comparatively imprecise CIs. CONCLUSIONS: Double FIT-positive individuals are significantly more likely to have a colonoscopy finding of incident CRC or premalignant polyp than single FIT-positive individuals. Clinicians and policymakers should consider updating their CRC screening protocols accordingly.