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Test Name:
C-Peptide, Serum or Plasma
- SBMF No:
30117 - Performance Lab Name:
Automated Lab - Test Mnemonic:
C-PEPTIDE - ABN:
Not required - CPT Code:
84681 - LOINC Code:
1986-9 - Also Known As:
C Peptide - Spec Type:
Serum - Spec Container:
Gold top (SST) or red top (serum) tube - Alt Spec Type:
Plasma - Alt Spec Container:
Green top (lithium heparin) or Lavender top (EDTA) tube - Pref Vol:
1.0 mL - Min Vol:
0.5 mL - Fasting:
Yes - Patient Prep:
Fasting at least 12 hours is preferred - Spec Collect:
Routine venipuncture - Spec Process:
Clot 30 minutes
Promptly centrifuge 15 minutes
If sample not sent to SBMF on day collected:
– Immediately transfer serum to separate plastic tube
– Freeze and transport frozen - Spec Store Transport:
Refrigerated (24 hours) or frozen - Spec Stability:
After separation from cells:
4 hours room temperature (20-30°C)
24 hours refrigerated (2-8°C)
1 month frozen (-20°C) – Do not use frost-free units that undergo repeated freeze/thaw cycles - Spec Reject:
Heat inactivated sample - Methodology:
Solid-Phase, Competitive Chemiluminescent Enzyme Immunoassay - Use:
Evaluation of hypoglycemia: patients with insulinoma show elevated insulin and C-peptide; while patients with factitious hypoglycemia from exogenous insulin administration have low C-peptide and elevated insulin levelsEvaluation of residual beta cell function in insulin-dependent diabetics. Patients who have undergone insulin therapy develop anti-insulin antibodies that may interfere with insulin measurements - Clinical Significance:
Human C-peptide, originating from pancreatic b-cells, is a by-product of the enzymatic cleavage of proinsulin to insulin. In this process, insulin and C-peptide split from the prohormone and secreted into the portal circulation in equimolar concentrations. Although C-peptide does not have any known biological function, it can be used as an index to insulin secretion.Human C-Peptide is a 31 amino acid chain with a molecular mass of approximately 3,020 daltons. Metabolically inert, it originates in the pancreatic B-cells as a byproduct of enzyme cleavages of proinsulin to insulin. In this process, insulin and C-peptide are split from the prohormone and secreted into the portal circulation in equimolar concentrations. It is this fact that underlies the clinical interest in plasma determinations of C-Peptide.Within limits, C-Peptide levels can serve as a valuable index to insulin secretion. Thus, low C-Peptide levels are to be expected where insulin secretion is diminished, as in insulin-dependent diabetes or suppressed, as a normal response to exogenous insulin: whereas elevated C-Peptide levels may result from the increased B-cell activity observed in insulinomas.Accordingly, in the differential diagnosis of hypoglycemia, C-peptide determinations can be used to supplement insulin measurements as an index to pancreatic activity in the classic 72-hour fasting test, and as the sole indicator of pancreatic activity where insulin itself is administered to check for suppressibility. In addition, covert self-administration of insulin can be virtually ruled out as the cause of hyperinsulinemia by the finding of an elevated C-peptide level.Circulating anti-insulin antibodies are commonly encountered in patients who have undergone insulin therapy. These would typically interfere with immunoassays for insulin, making it impossible to use insulin measurements in this context to check on residual B-cell activity, even if treatment were temporarily suspended. C-peptide measurements have therefore been used as an alternative in this context, to yield information on the natural history of insulin-dependent diabetes, to indirectly monitor insulin secretion in the presence of anti-insulin antibodies, and to help settle on an appropriate course of treatment.C-peptide has also been measured as an additional means for evaluating glucose tolerance and glibenclamide-glucose tests. - Reference Range:
1.1-4.4 ng/mL - Additional Test Info:
Because metabolism of C-peptide differs from that of insulin, C-peptide levels are, at best, a semiquantitative index of insulin secretion. - Day Run:
Sun-Sat (daily) - Time Run:
2:00 pm - Time Reported:
8 hours - Test Type:
HORMONE
