Insulin is a peptide hormone secreted by the β cells of the pancreatic islets of Langerhans and maintains normal blood glucose levels by facilitating cellular glucose uptake, regulating carbohydrate, lipid and protein metabolism and promoting cell division and growth through its mitogenic effects. C-peptide is a byproduct created when insulin is produced. Both insulin and C-peptide are created from a larger molecule called proinsulin which undergoes enzymatic cleavage to become des-31,32-proinsulin and des-64,65-proinsulin and eventually, insulin and C-peptide (an inactive peptide chain).