C-peptide

Proinsulin schematic topological diagram

C-peptide is the part of the proinsulin molecule that is cleaved before insulin secretion. Its serum concentration corresponds to insulin secretion. It is not taken up by the liver and, as there is no C-peptide in the injected insulin, the results are not affected by the treatment. It crosses the glomerular membrane and therefore its concentration increases in renal insufficiency.