Effect of offering colonoscopy at the faecal immunochemical test (FIT) positivity threshold: a regression discontinuity analysis in older adults

Why clinicians should know about it

• Picked for Epidemiology (paper of the day, 19 July 2026).

Abstract

BACKGROUND: Colorectal cancer (CRC) screening programmes often use the faecal immunochemical test (FIT) to identify individuals for follow-up colonoscopy but evidence on its impact on CRC incidence remains limited. Using a regression discontinuity design (RDD), we investigated whether CRC screening affects CRC incidence among adults aged 71-75 years with FIT values close to the threshold-an age group not consistently included in screening programmes. METHODS: Using registry data from 2014 to 2024, we compared CRC incidence among screening participants aged 71-75 years with FIT values just above versus just below the 100-ng/ml referral threshold, where only those above were offered colonoscopy. We included 2773 individuals with borderline FIT values (80-120 ng/ml). An RDD was used to estimate the effect of colonoscopy referral based on FIT on CRC incidence at values close to the threshold while mitigating healthy-user bias. RESULTS: Over a median 8.4-year follow-up, 165 CRC cases were observed. As expected from the lead time, early incidence was higher in FIT-positive individuals offered colonoscopy but cumulative incidence later plateaued in this group while it continued to rise in FIT-negative individuals. After 10 years of follow-up, a reduction was seen between the groups from 12.1 to 6.6 cases per 1000 person-years, equivalent to 5.5 fewer cases (95% confidence interval: 1.44-9.56) per 1000 person-years, corresponding to a 45.5% reduction. CONCLUSION: CRC screening reduces CRC incidence among adults aged 71-75 years with FIT values close to the FIT threshold. This could guide cancer screening policies for an age group that is only eligible for screening in some countries.

Abstract as published, via PubMed.