C-Peptide, Blood



Quest Diagnostics Test Code: 372

A measurement of the C-Peptide levels in the blood can indicate how much insulin the body is producing. Because C-Peptide levels correspond only to insulin produced by the body, it can be a useful measurement for people who take insulin medication for Diabetes.

C-peptide (connecting peptide) is part of the proinsulin, the precursor of the insulin in insulin synthesis pathway. In one moment, proinsulin decays on insulin on one side and C-peptide on the other. C-peptide is produced by a beta cell of the pancreas and is useful for distinguishing diabetes mellitus type 1 and 2 because, in DM type 1, beta cells are mostly destroyed, and that is the main reason for the lack of insulin. In DM type 2, beta cells are viable, but their synthetic function is played out. In other words, they produce a reduced amount of insulin, and therefore C-peptide, which is not the case in DM type 1 where there isn’t any insulin nor C-peptide production. Measurement of C-peptide also gives information about endogenous insulin production in patients on insulin therapy. It is also useful for determining the source of insulin in hyperinsulinemic hypoglycemia (for example, distinguishing insulin-secreting tumors from exogenous insulin administration) and to check whether a tumor of the pancreas (insulinoma) is completely removed. For this test, blood is sampled, and there is the special preparation that lasts at least 8-10 hours before testing.

This test is performed in following conditions such as:

• Diabetes (to differ between diabetes types 1 and 2)
• DM type 2 and use exogenous insulin
• Insulinoma suspected
• Have had insulinoma
• Frequent hypoglycemia

Also Known As: Insulin C-Peptide, Proinsulin C-Peptide


Fasting for 12 hours prior to collection is required.


Specimen Collected
  • Blood
Estimated Time Taken

Turnaround time for the C-Peptide, Blood (Serum) test is typically 4-6 business days.