Variation in fecal hemoglobin concentrations: Cross-sectional analysis of a screening trial and a screening program in Sweden.

ObjectivesTo assess variation in fecal hemoglobin concentration according to year and season of fecal immunochemical test screening in Sweden, the detection rate of advanced neoplasia, and factors that could influence fecal immunochemical test positivity including sex, age, comorbidity, and laboratory testing quality.MethodsWe performed a cross-sectional analysis of participants in the fecal immunochemical test arm of the randomized controlled trial SCREESCO between March 2014 and December 2019 and of participants in the screening program of Stockholm-Gotland, Sweden, who underwent a one-sample fecal immunochemical test between October 2015 and October 2024.ResultsA total of 33,232 individuals from SCREESCO and 315,664 individuals from the Stockholm-Gotland screening program were included. Fecal immunochemical test hemoglobin concentrations were generally higher in the winter but this varied over calendar years. In SCREESCO, the median fecal immunochemical test concentration was 0.0 μg hemoglobin/g feces in December 2015, 1.0 μg hemoglobin/g feces in June and 5.0 μg hemoglobin/g feces in December 2016, and 0.0 μg hemoglobin/g feces in June 2017. This was paralleled by a similar variation in the Stockholm-Gotland screening program. In months with higher fecal immunochemical test positivity in SCREESCO, there was a higher number of colonoscopies and a lower rate of advanced neoplasia detected. Male sex, higher age, and higher comorbidity were also associated with higher fecal immunochemical test positivity.ConclusionsThe variation in the number of colonoscopies and detection rate of advanced neoplasia paralleled the seasonal variation in fecal immunochemical test and warrants further studies on seasonal variation of fecal immunochemical test to optimize fecal immunochemical test-based colorectal cancer screening.