C-peptide is a product which is formed when the hormone insulin is produced and released into the body. A C-peptide is a type of blood test which is carried out to find out the quantity of insulin, your body is producing. This test helps in diagnosing the type of diabetes, the patient is suffering from or whether he is insulin resistant. The test measures the level of this peptide in the blood. Insulin helps the body to use and control the amount of sugar in the blood. Insulin allows glucose to enter into the body cells, where it is used for generating energy. The level of C-peptide in the blood can show how much insulin is being made by the pancreas. C-peptide does not affect the blood sugar level in the body. A person whose pancreas does not make any insulin (type 1 diabetes) has a low level of insulin and C-peptide. A person with type 2 diabetes can have a normal or high level of C-peptide.