C-Peptide is a 31-amino acid single-chain peptide that is made when proinsulin is split into insulin and C-Peptide. They split before proinsulin is released from endocytic vesicles within the pancreas-one C-Peptide for each insulin molecule. C-Peptide is the middle segment of proinsulin that is between the N-terminal B-chain (30 amino acids) and the C-terminal A-chain (21 amino acids).

Unlike insulin, C-Peptide has no known physiological function. Due to the fact that C-Peptide has a 2-to-5-time longer half-life than insulin, there are higher concentrations of C-Peptide than insulin in the peripheral circulation. Therefore, plasma C-Peptide concentrations may reflect pancreatic insulin secretion more reliably than the level of insulin itself. C-Peptide is cleared from the body by the kidney, and, unlike insulin, urine concentrations are 20 - 50 times higher than in plasma. Unlike plasma insulin levels, which fluctuate in response to meals, measurement of the 24-hour urinary excretion of C-Peptide provides a useful monitor of average beta cell insulin secretion.

The level of C-Peptide has been used to assess the following clinical applications:

1. to assess the residual beta cell function in patients treated with insulin and to distinguish between types 1 and 2 diabetes. Of particular interest is its use to indicate the need for progression to insulin therapy in type 2 diabetes.
2. The diagnosis of factitious hypoglycemia. The surreptitious administration of insulin causes high insulin levels in the absence of elevated C-Peptide concentrations.
3. Insulinoma diagnosis, especially in patients treated with insulin. C-Peptide measurement is used in insulin suppression tests in euglycemic patients with suspected insulinoma. Elevated C-Peptide levels in this test are indicative of insulinoma.
4. As a marker for residual pancreatic tissue after pancreatectomy. In the case of insulinoma, C-Peptide measurement may be used to detect metastasis and the response to therapy. It may also be used to monitor the progress of pancreas or islet cell transplantation

• Strip plates and additional reagents allow for use in multiple experiments
• Quantitative protein detection
• Establishes normal range
• The best products for confirmation of antibody array data

Standard, Biotinylated C-Peptide peptide, and Positive Control should be stored at -20°C after arrival. Avoid multiple freeze-thaws. The remaining kit components may be stored at 4°C. Opened Microplate Wells and antibody (Item N) may be stored for up to 1 month at 2° to 8°C. Return unused wells to the pouch containing desiccant pack and reseal along entire edge.