c peptide is an insulin-like molecule that is produced in the pancreas and acts as a precursor to insulin. It is also a very important molecule for the maintenance of normal glucose metabolism. In type 1 diabetes, c peptide levels decrease and insulin production is stopped or reduced as the result of the autoimmune destruction of the beta cells that produce insulin.
A c peptide test can help doctors determine whether someone has type 1 or type 2 diabetes. It can also help them see how well treatment is working if they are taking insulin or other medications that mimic the actions of insulin. The test is a simple blood test that is done in the doctor’s office or laboratory. A small needle is inserted into a vein in the arm to collect a blood sample for testing. The process is quick and painless, although some people experience a slight stinging sensation at the site where the needle was placed. A c peptide test can also be performed using urine that has been collected over 24 hours in a special container provided by the healthcare provider.
A high c peptide level with low blood glucose can indicate the presence of an insulin-producing tumor (insulinoma) in the pancreas. It can also be caused by the use of certain medications such as sulfonylureas that act like insulin. If a c peptide level remains high after an insulinoma is removed, it can indicate that the tumor has returned.