Equimolar amount of insulin and C peptide are usually released into the body system circulation under normal circumstances. A large fraction of circulating insulin is typically rapidly remove by the liver while the liver clear only a negligible amount of C peptide. C peptide is primarily cleared by the kidney at a lower metabolic clearance rate.
Normally the, C peptide level increases when the pancreatic secretion of insulin increases and vice versa. Therefore, exogenous administration of insulin results in an increase in insulin level without a corresponding increase in C peptide level. On the other hand, both insulin and C peptide levels are elevated in patients with insulinoma.