C-Peptide – 010108

This immunoassay is intended for the in vitro quantitative determination of C-peptide in human serum, plasma, and urine. The assay is intended for use as an aid in the diagnosis and treatment of patients with abnormal insulin secretion.

C-peptide is a single chain 31-amino acid (AA 33-63) connecting (C) polypeptide with a molecular weight of approximately 3021 daltons.^2,3 In the process of biosynthesis of insulin, the C-peptide is formed as a byproduct together with insulin by the proteolytic cleavage of the precursor molecule proinsulin, stored in secretory granules in the Golgi complex of the pancreatic β-cells. Proinsulin, in turn, was cleaved from preproinsulin.^3,4

C-peptide fulfills an important function in the assembly of the two-chain insulin (α- and β-chain) structure and the formation of the two disulfide bonds within the proinsulin molecule. Insulin and C-peptide are secreted in equimolar amounts and released into circulation via the portal vein.⁵ As half of the insulin, but almost none of the C-peptide, is extracted in the liver, C-peptide has a longer half-life (about 35 minutes) than insulin; 5 to 10 times higher concentration of C-peptide persist in the peripheral circulation, and these levels fluctuate less than insulin.