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

## TL;DR

This study found that fecal hemoglobin concentrations vary seasonally and over time in Sweden, which may impact colorectal cancer screening outcomes.

## Contribution

The study identifies seasonal and temporal variations in fecal immunochemical test results and their implications for screening effectiveness.

## Key findings

- Fecal hemoglobin concentrations were higher in winter months and varied across calendar years.
- Higher fecal immunochemical test positivity was associated with male sex, older age, and higher comorbidity.
- Seasonal variations in test results correlated with colonoscopy rates and detection of advanced neoplasia.

## Abstract

To 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.

We 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.

A 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.

The 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.