What is being tested?This test measures the level of C-peptide in a blood or urine sample. C-peptide and the
hormone insulin are created from a larger molecule called proinsulin, and stored in the beta cells of the pancreas. When insulin is released into the bloodstream to help transport glucose into the body's cells (to be used for energy), equal amounts of C-peptide also are released. This makes C-peptide useful as a marker of insulin production.
C-peptide can be used to help evaluate the production of endogenous insulin (insulin made by the body's beta cells) and to help differentiate it from exogenous insulin (insulin that is not produced by the body, e.g. injected insulin). This differentiation can be used to help diagnose and monitor a variety of conditions.
