Calibrator 18 is a lyophilized blend of 6 proteins: BDNF, C-Peptide, GLP-1 (9-36) [used for GLP-1 (inactive) and (total)], FGF-21, des-acyl Ghrelin, and PYY (1-36). It is intended for use as an assay calibrator for MSD U-PLEX mouse and rat assays that measure any of the included analytes. The utility of this product has not been evaluated in other applications. Individual analyte concentrations are provided in the lot-specific certificates of analysis. Human GLP-1 (9-36) and des-acyl Ghrelin were synthesized, as were mouse C-Peptide and PYY (1-36). Human FGF-21 was expressed in E. coli, and human BDNF was expressed in an insect cell line.