Proinsulin calibrator was developed for use as an assay calibrator for MSD U-PLEX assays that measure human Proinsulin. Human Proinsulin (25-110) was expressed in E. coli. 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. There are instructions on using this calibrator in the U-PLEX Metabolic Group 1 Human Product Inserts.