Clinical Information

Human C-peptide is a single chain polypeptide consisting of 31 amino acids. It connects the A and B chains of insulin in the precursor molecule proinsulin, which is stored in secretory granules of the pancreatic β-cells. In insulin biosynthesis, it facilitates the formation of the correct secondary and tertiary structure of the hormone. C-peptide and insulin are secreted in equimolar amounts; however, C-peptide does not undergo significant hepatic extraction but is renally eliminated and therefore persists longer in the peripheral circulation. This results in a longer half-life (> 30 minutes) and less fluctuation of C-peptide compared to insulin (5 minutes). Hence, measurements of C peptide more accurately reflect pancreatic insulin secretion rates than insulin. Moreover, C-peptide concentration is independent of exogenous insulin and is not subject to interference from insulin autoantibodies induced by insulin therapy.

C-peptide is used as a test of β-cell function human subjects in a variety of conditions including type 1 diabetes, and to aid in the differential diagnosis of hypoglycemia, and surreptitious insulin self-administration. A low C-peptide level is expected if the insulin secretion is diminished as in insulin-dependent diabetes (type 1 diabetes, latent autoimmune diabetes of adults (LADA)). Elevated C-peptide levels may be found when β-cell activity is increased as in hyperinsulinism and insulinomas.