Measurement of C-peptide may be useful in the differential diagnosis of spontaneous hypoglycaemia and as an aid to distinguish type 1 and type 2 diabetes mellitus (DM) by the assessment of residual beta-cell function. It may also be used in type 2 DM to determine the requirement for insulin therapy with disease progression.
C-peptide is a single chain 31-amino acid connecting (C) polypeptide with a molecular weight of approximately 3021 daltons. In the process of biosynthesis of insulin the C-peptide is formed as a by-product together with insulin by the proteolytic cleavage of the precursor molecule proinsulin. C-peptide fulfils an important function in the assembly of the two-chain insulin (A- and B-chain) structure and the formation of the two disulfide bonds within the proinsulin molecule. Insulin and C-peptide are secreted in equimolar amounts and released into circulation via the portal vein. C-peptide has a longer half-life (about 35 min) than insulin, with 5 to 10 times higher concentrations of C-peptide in the peripheral circulation. 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. Elevated C-peptide levels may result from increased β-cell activity observed in hyperinsulinism, renal insufficiency, and obesity. Decreased C-peptide levels are observed in starvation, factitious hypoglycemia, hypoinsulinism, Addison’s disease and after radical pancreatectomy.
0.34 – 1.8 nmol/L
- Type 1 and type 2 diabetes
Patient should be fasted; if patient undergoing investigation for hypoglycaemia then the specimen must be taken during a hypoglycaemic episode.
SST (yellow top) serum tube required. The specimen must be delivered to the laboratory with 30 minutes of venepuncture.