Insulin and C-Peptide

The Insulin and C‑Peptide test (also known as the C‑peptide and insulin profile) assesses endogenous insulin secretion and pancreatic beta‑cell function by comparing paired insulin and C‑peptide concentrations. When reviewed alongside plasma glucose, the profile aids evaluation of hypoglycemia and supports the diagnosis of insulinoma. It is used to monitor endogenous insulin production in diabetes, to gauge insulin resistance, and to inform treatment choices in type 2 diabetes, including whether to initiate insulin therapy or oral hypoglycemic agents. C‑peptide is not affected by insulin antibodies and remains informative when patients are receiving exogenous insulin.

Pancreatic beta cells synthesize insulin, and secretion rises as blood glucose increases after meals. Insulin facilitates cellular uptake of glucose and promotes hepatic glycogen formation; when glucose is abundant, surplus substrate is directed toward lipogenesis. Inadequate insulin production or impaired action reduces cellular glucose use and produces hyperglycemia, which over time contributes to complications affecting the kidneys, cardiovascular system, nervous system, and vision. Type 1 diabetes reflects absolute insulin deficiency, while type 2 diabetes is characterized predominantly by insulin resistance with a relative impairment in secretion. Hyperinsulinemia can precipitate or accompany hypoglycemia and may result from exogenous insulin administration or from autonomous secretion by an insulinoma.