C-Peptide

Alias: Insulin connecting peptide

Specimen Requirement: Fasting or two hour postprandial serum.

Container: Red-Black Speckled top, serum separator tube

Transport: Freeze serum if not transported to laboratory for immediate analysis.

Reference Range:

• Adult (fasting): 3.5-5.0 pg/mL
• Children (fasting): 500-2,500 pg/mL
• 2 hour postprandial: 2,200-6,500 pg/mL

Test Availability: Send out. Monday - Friday before 3:00 p.m.

Clinical Utilization:

1. Differential diagnosis of insulinoma. Order to assist diagnosis.
2. Assessment of beta-cell function in diabetes
3. Not indicated for healthy subjects - use insulin instead

Method of Analysis: Radioimmunoassay

Identifying Codes:

Hermann Test Code:

CPT Code:

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Interpretation:

The presence of C-peptide distinguishes endogenous insulin secretion from exogenous insulin administration, since insulin is synthesized endogenously in the beta-cells of the pancreas as proinsulin containing the C-peptide. In exogenous insulin the proinsulin has been activated and the C-peptide removed. Thus C-peptide is the best way to assess beta-cell function in patients with diabets mellitus. The concentration of C-peptide will be low or absent in patients with insulin-dependent diabetes mellitus (type I); whereas its concentraion will be normal or elevated in non-insulin-dependent diabets mellitus (Type II).

The measurement of C-peptide can also differentiate whether the cause of a hypoglycemia episode is due to endogenous surge of insulin (e.g. insulinoma) or injected insulin. In factitious hypoglycemia due to insulin injection, C-peptide will be low; whereas in endogenous insulin production, C-peptide will be elevated. However, differential diagnosis must be made whether the endogenous production of insulin is drug induced.