Performance of Faecal Immunochemical Testing for Colorectal Cancer Screening at Varying Positivity Thresholds.

Background: The positivity thresholds of faecal immunochemical testing (FIT) in colorectal cancer (CRC) screening vary between countries.

Aims: To explore the trade-off between colonoscopies performed, adverse events and lesions detected at different FIT thresholds in a Norwegian CRC screening trial.

Methods: We included first participation in biennial FIT screening for 47,265 individuals aged 50-74 years. Individuals with FIT > 15 μg Hb/g faeces were referred for colonoscopy. We estimated the number of colonoscopies, adverse events, screen-detected CRCs, advanced adenomas and serrated lesions expected at FIT thresholds currently or recently used in other European countries ranging between 20 and 150 μg/g.

Results: At the 15 μg/g threshold (Norway), 3705 participants underwent colonoscopy, of whom 203 had CRC, 1119 advanced adenomas and 256 advanced serrated lesions. Using a 47 μg/g threshold, 1826 (49.3%) individuals would have undergone colonoscopy, and 154 (75.9%) would have been diagnosed with CRC, 702 (62.7%) with advanced adenoma and 128 (50.0%) with advanced serrated lesion compared to the 15 μg/g threshold. At 150 μg/g, the corresponding figures would have been 838 (22.6%) undergoing colonoscopy, 114 (56.2%) with CRC, 345 (30.8%) advanced adenoma and 54 (21.1%) advanced serrated lesions. The detection rate of stage I CRC was 0.22% at 15 μg/g and 0.11% at 150 μg/g. Post-colonoscopy bleeding rates were 0.8% and 1.7%, respectively.

Conclusions: Increasing the FIT threshold reduces colonoscopy demand, but substantially decreases lesion detection and unfavourably changes CRC stage distribution. The risk of adverse events at colonoscopy increased with FIT threshold, requiring country-specific information on adverse events.

Trial registration: Clinicaltrials.gov identifier: NCT01538550.