C-peptide test is used as a tool to test the occurrence of type 1 and type 2 diabetes. The C-peptide released by the Beta cells of pancreas even though have no association with diabetes, its measurement can reveal the amount of insulin production from the cells.

C-peptide can be used for the following purposes:

• To find out whether one have type 1 or type 2 diabetes
• When one have type 1 diabetes and the doctor needs to know how much insulin the pancreas still makes
• To find out if it is time to start insulin in a patient with type 2 diabetes
• To find out why one have low blood sugar (hypoglycemia)
• To diagnose a tumor of the pancreas that releases insulin, called an insulinoma
• If one have had the pancreas removed

The test typically uses a blood or urine sample. A normal C-peptide range is 0.5 to 2.0 nanograms per milliliter.

A high level of C-peptide indicates the following:

• Have insulin resistance; if have type 2 diabetes
• Have insulinoma (or)
• Have kidney disease
• Uptake of high doses of sulfonylureas

A low C-peptide level indicates:

• Type 1 or type 2 diabetes
• Taking insulin shots and it is suppressing the release of insulin from pancreas
• Have low blood sugar
• Treatment has shrunk insulinoma