Colorectal cancer screening programme: is the French faecal immunological test (FIT) threshold optimal?

BACKGROUND: In France, the colorectal cancer organised screening programme uses the faecal immunological test. A positive test ⩾30 μg Hb/g of stool leads to a colonoscopy for identification of potential colorectal lesions. Cut-off values vary from 20 to 47 μg Hb/g of stool in Western countries. We herein question this threshold’s relevance in a French population and perform a retrospective observational study using the Parisian database between 1 April 2015 and 31 December 2018. METHODS: Rates of participation, numbers of positive faecal immunological test (FIT), detection rates and positive predictive values for advanced adenomas and/or colorectal cancer were determined. Mean positivity values for colorectal lesions were calculated. RESULTS: In our population, there were 4.1% positive tests and 67.6% colonoscopy results available with final reports. Positive predictive value for advanced adenomas and colorectal cancer were 30% [95% confidence interval (CI) 29.8–30.3] and 7.4% (95% CI 7.35–7.52), respectively. The mean positivity value for all positive tests in our population was 101.7 µg Hb/g of stool (95% CI 85–118.3). There were 1136 normal colonoscopies (21.4%) with a mean positivity value of 88.6 μg Hb/g of stool. Following a negative test in a first screening campaign, 40.8% of patients in our population performed a second test with a positivity rate of 1.3% and with the encounter of 81 colorectal cancers. The risk of having a positive test during the second screening campaign and finding advanced colorectal lesions significantly increased (all p < 0.001) when comparing negative FIT results ranging between 15 and 29 μg Hb/g of stool to 0 and 14 μg Hb/g of stool from the previous campaign. CONCLUSION: Using the current positivity threshold, some patients were considered negative with a delay in colorectal cancer diagnosis, suggesting the threshold could be lowered. Also, the mean positivity value for normal colonoscopies was high, raising the question of upper gastrointestinal bleeding.