Standardisation Challenges in ELISA-Based Quantification of Equine Chorionic Gonadotropin (eCG/PMSG)

Equine chorionic gonadotropin (eCG/PMSG) is widely used for female-cycle synchronization and estrus induction in livestock and in biomedical research, where reliable quantitative assessment is increasingly important. However, its structural and glycosylation heterogeneity complicates antibody-based measurement and assay standardization. This Technical Note evaluated six commercially available quantitative PMSG ELISA kits representing three distinct analytical profile groups. Kit-provided calibration standards were characterized by Western blotting, Coomassie staining, and LC-MS/MS, while quantitative performance was assessed using serial dilutions of two commercial PMSG preparations. DRG, Creative Diagnostics, and Demeditec showed similar calibration-standard profiles and concentration-dependent responses, although measured concentrations were consistently below nominal values. Biomatik and MyBiosource displayed closely related analytical profiles but little meaningful concentration-dependent response, whereas Krishgen measurements remained within a narrow range despite changes in nominal PMSG input. The calibration standards differed substantially in protein composition, and no eCG-derived peptides were identified by LC-MS/MS under the conditions used. These findings demonstrate that quantitative results obtained with commercially available PMSG ELISAs are not necessarily comparable and may be strongly influenced by calibration-material composition, assay format, and matrix effects. The findings highlight the limitations of current quantitative PMSG assays and the need for a well-characterized, commutable reference material, together with assay-specific validation of dilution parallelism and analyte recovery, to improve the reliability and comparability of eCG/PMSG measurements.