Applicability of Commercially Available ELISA Kits for the Quantification of Faecal Immunoreactive Corticosterone Metabolites in Mice

Background: Commercially available ELISA kits are popular among investigators that quantify faecal corticosterone or cortisol metabolites (FCM) for stress assessment in animals. However, in faeces, these assays mainly detect immunoreactive glucocorticoid metabolites. Since different assays contain antibodies of different origin, the detection level and cross-reactivity towards different metabolites and other steroids differ considerably between assays. Thus, the validity of one assay for FCM quantification in stress assessment is not necessarily the same for another assay. Materials and Methods: The present study was designed to investigate corticosterone (CORT) in serum and FCM levels in faeces of laboratory mice, as quantified in four different ELISA kits (DRG EIA-4164, Demeditec DEV9922, Enzo ADI-900-097 and Cayman EIA kit 500655). Assay kits were chosen based on the origin of the antibody, detection level and variation in cross-reactivity. Results: As expected, all four assay kits could detect higher serum CORT levels in mice treated with adrenocorticotropic hormone (ACTH), compared to untreated mice. Unexpectedly though, the measured concentration of serum CORT differed significantly between assays, in both groups of mice. In faecal samples, there was no consistent positive correlation between the levels detected in the four assays and the measured concentration of FCM also differed between assays. Conclusion: Whereas commercially available CORT ELISAs are frequently successfully used for FCM quantification, validation of the assays is necessary as all assays do not work well under all circumstances. In this study, the ELISAs could determine relative differences in serum CORT levels and FCM levels between samples; however, the fidelity of the measurements to the true concentrations was low.