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HelpCatalog ID CPEP C-Peptide
Specimen Requirements
Serum in Gold or Red Top Tube, 1 ml serum / 2mL whole blood
Storage and Transport
Room temperature: 8 hours
Refrigerated: 48 hours
Causes for Rejection
Grossly hemolyzed; grossly lipemic; quantity insufficient; wrong tube
Reference Range
Adult Reference Range: 0.78 - 5.19 ng/mL
Pediatric reference ranges have not been formally verified for pediatric patients. Published literature indicates that reference intervals for adult and pediatric patients are comparable.
Useful For
Diagnostic workup of hypoglycemia:
-Diagnosis of factitious hypoglycemia due to surreptitious administration of insulin
-Evaluation of possible insulinoma
-Surrogate measure for the absence or presence of physiological suppressibility of endogenous insulin secretion during diagnostic insulin-induced hypoglycemia (C-peptide suppression test)
Assessing insulin secretory reserve in selected diabetic patients (as listed below) who either have insulin autoantibodies or who are receiving insulin therapy:
-Assessing residual endogenous insulin secretory reserve
-Monitoring pancreatic and islet cell transplant function
-Monitoring immunomodulatory therapy aimed at slowing progression of preclinical, or very early stage type 1 diabetes mellitus
Interpretation
To compare insulin and C-peptide concentrations (ie, insulin to C-peptide ratio):
-Convert insulin to pmol/L: insulin concentration in mcIU/mL x 6.945 = insulin concentration in pmol/L
-Convert C-peptide to pmol/L: C-peptide concentration in ng/mL x 331 = C-peptide concentration in pmol/L
Factitious hypoglycemia due to surreptitious insulin administration results in elevated serum insulin levels and low or undetectable C-peptide levels, with a clear reversal of the physiological molar insulin to C-peptide ratio (≤1) to an insulin to C-peptide ratio of greater than 1. By contrast, insulin and C-peptide levels are both elevated in insulinoma and the insulin to C-peptide molar ratio is 1 or less. Sulfonylurea ingestion also is associated with preservation of the insulin to C-peptide molar ratio of 1 or less.
In patients with insulin autoantibodies, the insulin to C-peptide ratio may be reversed to greater thsn 1, because of the prolonged half-life of autoantibody-bound insulin.
Dynamic testing may be necessary in the workup of hypoglycemia; the C-peptide suppression test is most commonly employed. C-peptide levels are measured following induction of hypoglycemia through exogenous insulin administration. The test relies on the demonstration of the lack of suppression of serum C-peptide levels within 2 hours following insulin-induced hypoglycemia in patients with insulinoma.
Performing Lab & Turn-Around-Time
Core Laboratory, AD 3301, 706-721-2120
Results typically available <2 hours from laboratory specimen receipt.
CPT Code
84681