Calibrator 13 is a lyophilized blend of 8 human proteins: GLP-1 (9-36), GIP (3-42), FGF-21 (29-209), Leptin (22-167), Pancreatic Polypeptide (PP), PYY (3-36), Desghrelin, and Glucagon. It was developed for use as an assay calibrator for MSD U-PLEX human assays that measure GLP-1 (total), GLP-1 (inactive), GIP (total), GIP (inactive), FGF-21, Leptin, PP, PYY (total), Ghrelin (total), and Glucagon. The utility of this product has not been evaluated in other applications. The amount of each analyte is provided in the lot-specific certificates of analysis. Calibrator 13 includes synthetic GLP-1 (9-36) [for both GLP-1 (total) and GLP-1 (inactive) assays], GIP (3-42) [for both GIP (total) and GIP (inactive) assays], PP, PYY (total), and Desghrelin. It also includes FGF-21, Glucagon, and Leptin which were recombinantly expressed in E. coli. Instructions on using Calibrator 13 in U-PLEX assays are provided in the U-PLEX Metabolic Group 1 Human Product Inserts.