Also known as: Connecting Peptide, Insulin C-Peptide, Proinsulin C-Peptide.

A C-peptide test will measure the level of this peptide in the blood. The peptide is generally found in amounts equal to insulin because insulin and C-peptide are linked when first made by the pancreas. Insulin helps the body use and control the amount of glucose (sugar) in the blood and allows glucose to enter body cells where it is used for energy. The level of C-peptide in the blood may show how much insulin is being made by the pancreas. C-peptide doesn't affect the blood sugar level in the body. A C-peptide test can be done when diabetes has just been discovered and it is not clear whether type 1 diabetes or type 2 diabetes is present. A person whose pancreas does not make any insulin (type 1 diabetes) will have a low level of insulin and C-peptide. A person with type 2 diabetes will have a normal or high level of C-peptide. A C-peptide test is done to:

1. Help differentiate between type 1 diabetes and type 2 diabetes.
2. Find the cause of hypoglycemia.
3. Check to see whether an insulinoma was completely removed.