C-peptide
Also known as: Insulin C-peptide; Connecting peptide
Formal name: C-peptide
The Test Sample
What is being tested?
This test measures the level of C-peptide in a blood or urine sample. Proinsulin is the inactive precursor of insulin and is synthesized in the beta cells of the pancreas. Cleavage of proinsulin produces insulin and C-peptide, which are stored in the beta cells. When insulin is required and released into the bloodstream to help transport glucose into the body’s cells (to be used in energy production), 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) and to help differentiate it from exogenous insulin (insulin that is not produced by the body and so does not generate C-peptide).
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm. If a 24-hour urine sample is required, you will be asked to save all of your urine over a 24-hour time period.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
You may need to fast before having this test performed. Ask your doctor for instructions.
