To quantify the endogenous insulin secretion, C‑peptide is measured basally, after fasting and after stimulation and suppression tests. Due to high prevalence of endogenous anti‑insulin antibodies C‑peptide concentrations reflect the endogenous pancreatic insulin secretion more reliably in insulin‑treated diabetics than the levels of insulin itself.
Measurements of C‑peptide may therefore be an aid in the assessment of a residual β‑cell function in the early stages of type‑1 diabetes mellitus and for the differential diagnosis of latent autoimmune diabetes of adults (LADA) and type‑2 diabetes. C‑peptide measurements are also used to assess the success of islet transplantation and for monitoring after pancreatectomy.
