Are fecal immunochemical test characteristics influenced by sample return time a population-based colorectal cancer screening trial

Objectives: Fecal immunochemical tests (FIT) are preferred over guaiac-based fecal occult blood testing as colorectal cancer (CRC) screening tool. However, hemoglobin (Hb) degradation over time may influence FIT outcome. We therefore evaluated the effect of sample return time on FIT performance characteristics in a population-based CRC screening trial. Methods: A representative random sample of the Dutch population (n=17,677), aged 50-74 years, was invited for FIT screening (OC-Sensor Micro; cutoff 50 ng Hb/ml). Sample return time was defined as the interval in days between fecal sampling and FIT laboratory delivery. Moreover, a random sample of positive FITs were selected to be stored at room temperature and re-tested every 3-4 days. Results: In total, 8,958 screenees fulfilled our inclusion criteria. The mean sample return time was 3 days (±3). Overall, 792 screenees (8.8%) had a positive test. Between the sample return time groups, the positivity rate (PR) varied between 7.7 and 9.0%. No statistically significant associations were found between PR or detection rate (DR) and the different sample return time groups (P value=0.84 and 0.76, respectively). For the laboratory experiment, 71 positive FITs were stored at room temperature and re-tested with standard intervals. The mean daily fecal Hb decrease was 5.88% per day (95% confidence interval 4.78-6.96%). None of the positive FITs became negative before 10 days after fecal sampling. Conclusions: This population-based CRC screening trial demonstrates that both the PR and DR of FITs do not decrease with prolonged sample return times up to 10 days. This means that a delay in sending the FIT back to the laboratory, of up to at least 1 week, does not necessitate repeat sampling in case of a negative test result. These data support the use of FIT-based screening as a reliable tool for nationwide CRC screening programs.