C-peptide is a protein that is produced when proinsulin is split into insulin and C-peptide in the pancreas. Proinsulin is a precursor molecule to insulin, which is released into the bloodstream to regulate blood sugar levels. C-peptide is released into the bloodstream at the same time as insulin, so measuring the level of C-peptide can provide information about insulin production.
C-peptide testing is often used to help diagnose and monitor diabetes. In type 1 diabetes, the immune system attacks and destroys the cells in the pancreas that produce insulin. As a result, people with type 1 diabetes have low or undetectable levels of C-peptide. In type 2 diabetes, the body becomes resistant to insulin, and the pancreas may produce more insulin than normal in response. Measuring C-peptide levels can help distinguish between the two types of diabetes.
C-peptide testing may also be used to monitor the effectiveness of treatments for diabetes, such as insulin therapy or medications that increase insulin production. If insulin therapy is successful, C-peptide levels should increase as well.
In addition to diabetes, C-peptide testing may be used in other medical conditions, such as insulinomas (tumors of the pancreas that produce insulin), and to evaluate pancreatic function after surgery or injury.
