Calibrator 15 is a lyophilized blend of 2 human proteins: insulin and C-Peptide. It was developed for use as an assay calibrator for MSD U-PLEX human assays that measure insulin and C-Peptide. 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. Insulin was expressed in E. coli. C-Peptide was synthesized. Instructions on using Calibrator 15 in U-PLEX assays are provided in the U-PLEX Metabolic Group 1 Human Product Inserts.