C-peptide is a peptide which is made when proinsulin is split into insulin and C-peptide. They split when proinsulin is released from the pancreas into the blood in response to a rise in serum glucose - one C-peptide for each insulin molecule.C-peptide is the abbreviation for "connecting peptide", although its name was probably also inspired by the fact that insulin is also composed of an "A" chain and a "B" chain. C-peptide was discovered in 1967. The first documented use of the C-peptide test was in 1972. It should not to be confused with c-reactive protein or Protein C.C-peptide functions in repair of the muscular layer of the arteries. C-peptide also exerts beneficial therapeutic effects on many complications associated with diabetes mellitus, such as for instance diabetic neuropathy and other diabetes-induced ailments. In the kidneys, C-peptide prevents diabetic nephropathy, and in the heart blood flow is improved in diabetic patients.