C-Peptide

Connecting Peptide Assay (C-Peptide), Insulin C-Peptide

Results

A C-peptide test measures the level of this peptide in the body.

Normal

Normal values vary from lab to lab. The level of C-peptide in the blood must be read with the results of a blood glucose test. Both these tests will be done at the same time.

C-peptide

Fasting:	0.78–1.89 nanograms per milliliter (ng/mL) or 0.26–0.62 nanomoles per liter (nmol/L)

High values

• High levels of both C-peptide and blood glucose are found in people with type 2 diabetes or insulin resistance (such as from Cushing's syndrome).
• A high level of C-peptide with a low blood glucose level may mean an insulin-producing tumor of the pancreas (insulinoma) is present or that the use of certain medicines such as sulfonylureas or meglitinides is causing the high level.
• 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 (metastasized).

Low values

• Low levels of both C-peptide and blood glucose are found in liver disease, a severe infection, Addison's disease, or insulin therapy.
• A 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 so low it cannot be measured. The blood glucose level will be high, and insulin will be needed in order for the person to survive.

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Author:	Caroline Rea, RN, BS, MS	Last Updated: July 28, 2008
Medical Review:	Caroline S. Rhoads, MD - Internal Medicine Alan C. Dalkin, MD - Endocrinology
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