Performance of the fecal immunochemical test is not decreased by high ambient temperature in the rapid return system.

Background: Hemoglobin concentration of fecal immunochemical test may be decreased at high ambient temperature, and fecal samples in FIT may be exposed to high ambient temperature.

Aims: The aim of this study was to determine whether a high ambient temperature on the day of screening may decrease the performance of FITs in population-based screening.

Methods: We performed FITs for asymptomatic participants aged 50 years or older. Fecal hemoglobin concentration, the probability of a positive FIT and a detection rate of colorectal neoplasms were compared between low (<10.0 °C) and high (≥25.0 °C) temperature groups.

Results: The FIT results for 8,316 participants were analyzed. The mean log(10) Hb concentration in the low temperature group was significantly higher than those in the high temperature group (0.36 vs. 0.25 ng/ml, p = 0.000). Regression analysis showed that an increase in temperature of 1 °C reduced the probability of a positive FIT by 3.1 %. However, we found no differences between the two groups in the FIT positive rate and detection rate of colorectal neoplasms. In multivariate analysis, high ambient temperature was not a significant risk factor for either the positive FIT result or the detection of colorectal neoplasms.

Conclusions: Potential instability of fecal hemoglobin at high ambient temperatures should be considered; however, its influence on performance of FIT may be attenuated by the short exposure time of fecal samples to high ambient temperature (i.e., rapid return system).