C-Peptide 

Updated: Dec 04, 2014
  • Author: Georges Elhomsy, MD, ECNU, FACE; Chief Editor: Eric B Staros, MD  more...
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Reference Range

C-peptide is a peptide composed of 31 amino acids. It is released from the pancreatic beta-cells during cleavage of insulin from proinsulin. It is mainly excreted by the kidney, and its half-life is 3-4 times longer than that of insulin.

The reference range of C-peptide is 0.8-3.1 ng/mL (conventional units), or 0.26-1.03 nmol/L (SI). [1]

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Interpretation

C-peptide levels are elevated in the following:

C-peptide levels are suppressed in the following:

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Collection and Panels

Collection details are as follows:

  • Patient instructions: Overnight fasting is indicated
  • Specimen type: Serum
  • Collection tube: Red-top tube or gel-barrier tube
  • Unacceptable conditions: Grossly hemolyzed specimens
  • Specimen preparation: Separate serum from cells and transfer to transport tube
  • Storage/transport temperature: Refrigerated
  • Stability: Refrigerated, 2 weeks; Frozen, 2 weeks
  • Panels: None
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Background

Description

C-peptide is a peptide composed of 31 amino acids. It is released from the pancreatic beta-cells during cleavage of insulin from proinsulin. It is mainly excreted by the kidney, and its half-life is 3-4 times longer than that of insulin.

The insulin precursor, preproinsulin, is produced in the rough endoplasmic reticulum of pancreatic beta-cells and is later cleaved to proinsulin and transported to the Golgi apparatus, where is packed into secretory granules. During maturation of this granules, proinsulin is cleaved into 3 peptide chains—insulin (2 chains, A and B) and C-peptide.

Although, historically, C-peptide was considered to have no biologic activity; recent studies suggest that C-peptide may improve capillary blood flow in the feet, decrease urinary albumin excretion, and improve nerve function in individuals with type 1 diabetes. [2, 3] } [4, 5]

Indications/Applications

C-peptide should be measured in the combination of insulin and proinsulin as part of the workup for nondiabetic hypoglycemia to differentiate between insulin-dependent hypoglycemia (high C-peptide levels) versus insulin-independent hypoglycemia (low C-peptide levels). For appropriate interpretation of these tests, low serum blood glucose levels (< 55 mg/dL; preferably < 45 mg/dL) should be documented in the same blood sample.

In combination with serum and/or urine sulfonylurea screening, C-peptide testing can help differentiate between factitious hypoglycemia due to exogenous insulin use (low C-peptide level, high insulin level) and sulfonylurea intoxication (high C-peptide level, high insulin level).

C-peptide can also be used for the following:

  • To monitor pancreatic function after a pancreatic transplantation or pancreatectomy
  • To monitor beta-cell function in a patient with early-stage type 1 diabetes mellitus who is receiving immunomodulatory therapy to slow disease progression
  • To differentiate between type 2 diabetes mellitus and latent autoimmune diabetes of adults (LADA)
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