C-Peptide

C-Peptide is increased in hypoglycemic patients with insulin-secreting neoplasms (also increased levels of endogenous insulin), and decresased in hypoglycemic patinets with low C-peptide levels in the presence of high exogenous insulin. Assessment of  C-peptide is also useful in insulin-dependent diabetics in cases when antibodies to insulin are produced.
Type 1 Diabetes (Insulin dependent): The insulin-producing beta cells of the pancreas are almost completely demaged and do not produce insulin.
Type 2 Diabetes (Non-insulin dependent): The insulin-producing beta cells of the pancreas produce either not enough insulin or the body of the patients becames resistant to the effects of their own insulin.