What is C-Peptide?

C-peptide is a hormone produced by the pancreas, released at the same time as insulin. It has no effect on blood sugar but is a useful marker of insulin production, since the pancreas usually releases c-peptide and insulin in equal amounts.

Testing for c-peptide production can help doctors determine if someone has type 1 or type 2 diabetes. For a person with type 1 diabetes, c-peptide levels will be very low or undetectable because of a lack of insulin production; in type 2 diabetes, c-peptide levels may be normal or elevated in efforts to overcome insulin resistance.

Checking c-peptide levels requires a blood test and may also have fasting requirements (your doctor will let you know what you need to do). Low levels of c-peptide may indicate type 1 diabetes, Addison disease, or liver disease. High levels may indicate type 2 diabetes, insulin resistance, Cushing's syndrome, or a pancreatic tumor.

A c-peptide test provides useful information but is not used to diagnose diabetes.