Development and validation of a latex particle-enhanced turbidimetric immunoassay for fecal calprotectin Bioprocessing and Bioengineering

Background Fecal calprotectin (FCP) is a crucial non-invasive biomarker for diagnosing and monitoring inflammatory bowel disease (IBD). However, the standard enzyme-linked immunosorbent assay (ELISA) is time-consuming and labor-intensive. This study aimed to develop and evaluate a rapid, automated latex particle-enhanced turbidimetric immunoassay (LTIA) for FCP quantification. Methods Recombinant human S100A8 and S100A9 proteins (the subunits of calprotectin) were expressed in E. coli and purified. Polyclonal antibodies were generated in rabbits by immunization with these proteins. The antibodies were then covalently coupled to carboxylated latex particles (188 nm) to create the LTIA reagent. The linear repeatability, within-lab precision and interference substances of the reagent were determined, The performance of this method was evaluated using clinical fecal samples (n = 104), including linearity and correlation with commercial ELISA Kit (B Ü Hlmann fCAl). Results The developed LTIA demonstrated excellent linearity within the range of 50–1500 µg/g (R² = 0.9910). A strong correlation was observed between the new LTIA and the reference ELISA method, with a correlation coefficient (r) of 0.9830. The regression equation was y = 1.0359x + 8.8159. Bland-Altman analysis confirmed good agreement between the two methods, with 95.19% of data points within the 95% limits of agreement. Conclusion The LTIA showed strong correlation with the established ELISA for FCP quantification, offering a rapid, automated alternative potentially suitable for high-throughput labs. This study, completing development from antibody to reagent, supports its translational potential. However, this study has several limitations. Limitations include a single-center sample set, limiting generalizability, the need for multicenter validation, and unreported key analytical parameters such as LOD, LOQ, and inter-assay variation.