Sign in →

Catalog 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


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