C-Peptide

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

What To Think About

• A C-peptide test must be done at the same time as a blood glucose test. For more information, see the medical test Blood Glucose.
• A person with new type 2 diabetes often has a normal or high level of C-peptide in the blood. Over time, a person with type 2 diabetes may develop a low level of C-peptide.
• To help tell the difference between type 1 and type 2 diabetes and to help guide treatment, most doctors look at a person's age, weight, and how long symptoms have been present. In rare cases, a C-peptide stimulation test may be done to help tell the difference between the two types of diabetes. During a C-peptide stimulation test, a blood sample is taken to measure C-peptide. Then a shot of a hormone to increase blood sugar (glucagon) is given into a vein in the arm. Another blood sample is taken. In people with type 1 diabetes, C-peptide levels will be low because the pancreas cannot make any insulin in response to the glucagon. In people with type 2 diabetes, C-peptide levels will be higher than the first blood test because the pancreas is making more insulin in response to the glucagon.

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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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