OBJECTIVES

To systematically investigate and directly compare, for the first time, the sample stability of a large number of quantitative fecal immunochemical tests (FITs) at different storage conditions.

METHODS

Stool samples were obtained from participants of the German screening colonoscopy program between 2005 and 2010. After an initial FIT-based hemoglobin (Hb) measurement, stool samples were kept frozen at -80 °C until analysis. Twenty randomly selected participants with initial measurements ranging from 10 to 100 μg Hb/g feces were included. Ten quantitative FITs were investigated in parallel. A defined stool amount was extracted using each manufacturer's brand-specific fecal sampling device and stored at 5 °C, 20 °C, and 35 °C, respectively. After 1, 4, 5, and 7 days, the samples were analyzed blinded. Median fecal Hb concentrations and positivity rates were calculated.

RESULTS

Mean age of the participants was 67 years (range: 56-80 years) and 60% were male. The most advanced finding at screening colposcopy was advanced adenoma in five and non-advanced adenoma in eight cases. Hyperplastic polyps were found in two participants and five participants were without any findings. At 5 °C storage temperature, almost all FITs showed fairly stable results throughout the 7-day observation period. At 20 °C, most FITs still showed fairly stable results over 4 days, whereas positivity rates significantly declined from day 4 on for most FITs at 35 °C. Major differences regarding the sample stability between FITs were observed.

CONCLUSION

FIT-specific Hb decay according to ambient temperature and time period between sampling and test evaluation requires careful consideration in the design of FIT-based screening programs.