Serum C-peptide

Reference values (norm) for the concentration of C-peptide in the blood serum in adults are 0.78-1.89 ng/ml.

C-peptide is a fragment of the proinsulin molecule, the cleavage of which results in the formation of insulin. Insulin and C-peptide are secreted into the blood in equimolar quantities. The half-life of C-peptide in the blood is longer than that of insulin, so the C-peptide/insulin ratio is 5:1. Determination of the concentration of C-peptide in the blood allows one to characterize the residual synthetic function of beta cells in patients with diabetes mellitus. Unlike insulin, C-peptide does not cross-react with insulin antibodies, which allows one to determine the content of endogenous insulin in patients with diabetes mellitus by its level. Considering that insulin preparations do not contain C-peptide, its determination in the blood serum allows one to evaluate the function ofpancreatic beta cells in patients with diabetes mellitus receiving insulin. In a patient with diabetes mellitus, the basal level of C-peptide and especially its concentration after glucose loading (during OGTT) allows to establish the presence of resistance or sensitivity to insulin, to determine the phases of remission and thus to adjust therapeutic measures. During an exacerbation of diabetes mellitus, especially type 1, the concentration of C-peptide in the blood decreases, which indicates a deficiency of endogenous insulin.

In clinical practice, the determination of C-peptide in the blood is used to establish the cause of hypoglycemia. Patients with insulinoma have a significant increase in the concentration of C-peptide in the blood. To confirm the diagnosis, a C-peptide suppression test is performed. In the morning, the patient's blood is taken to determine the C-peptide. Then, insulin is administered intravenously for 1 hour at a rate of 0.1 U/kg and the blood is taken again. If the C-peptide level after insulin administration decreases by less than 50%, one can assume with a high degree of certainty the presence of an insulin-secreting tumor.

Monitoring of C-peptide levels is especially important in patients after surgical treatment of insulinoma; detection of elevated C-peptide levels in the blood indicates metastases or tumor recurrence.

Changes in serum C-peptide concentrations in various diseases and conditions

C-peptide is elevated

• Insulinoma
• Chronic renal failure

C-peptide is reduced

• Administration of exogenous insulin
• Diabetes mellitus type 1
• Diabetes mellitus type 2

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