Description
C-peptide test measures the level of this peptide in the blood. It is generally found in amounts similar to insulin due to the fact that insulin and C-peptide are linked when first made by the pancreas. Insulin helps the body control the amount of glucose in the blood. Insulin allows glucose to enter body cells where it is used for obtaining energy. 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.
Purpose of the test
The C-peptide test can be done when diabetes has just been found 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) has a low level of insulin and C-peptide. A person with type 2 diabetes has a normal to high level of C-peptide.
A C-peptide test can also help find the cause of low blood sugar, such as excessive use of medicine to treat diabetes or a noncancerous growth (tumor) in the pancreas (insulinoma). Because synthetic insulin does not have C-peptide, a person with a low blood sugar level from taking too much insulin will have a low C-peptide level. An insulinoma causes the pancreas to release too much insulin, which causes blood sugar levels to drop (hypoglycemia) . In this case, the patient will have a high level of C-peptide in the blood.
Reference range values
0.78-1.89 microg/L (0.26-0.62 nmol/L)
Abnormal findings
High
- High levels of both C-peptide and blood glucose are found with type 2 diabetes or insulin resistance (such as from Cushing's syndrome).
- High levels of C-peptide with a low blood glucose level may mean an insulin-producing tumor of the pancreas (insulinoma) is present or the use of certain medicines such as sulfonylureas or meglitinides.
- If C-peptide levels are high after an insulinoma is taken out, it may mean that the tumor has returned or that the tumor has spread to other parts of the body.
Low
- Low levels of both C-peptide and blood glucose are found in liver disease, Addison's disease, or insulin therapy.
- Low level of C-peptide with a high blood glucose level is found in people with type 1 diabetes.
- Complete removal of the pancreas (pancreatectomy) causes a C-peptide level very low. Blood glucose level will be high, and insulin will be needed in order for the person to survive.