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Test Code 0205757 C-Peptide, Serum

Additional Codes

Mayo Test ID
CPR

Performing Laboratory

Mayo Clinic Laboratories in Rochester

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

Method Name

Electrochemiluminescence Immunoassay

Reporting Name

C-Peptide, S

Specimen Type

Serum


Specimen Required


Patient Preparation:

1. Patient should fast for 8 hours.

2. For 12 hours before this test do not take multivitamins or dietary supplements containing biotin (vitamin B7), which is commonly found in hair, skin, and nail supplements and multivitamins.

Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 0.5 mL

Collection Instructions:

1. Serum gel tubes should be centrifuged within 2 hours of collection.

2. Red-top tubes should be centrifuged and aliquoted within 2 hours of collection.


Specimen Minimum Volume

0.4 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Frozen (preferred) 30 days
  Refrigerated  7 days

Reject Due To

Hemolysis

Mild OK; Gross reject

Lipemia

Mild OK; Gross OK

Icterus

NA

Other

Autopsy specimen

Reference Values

1.1-4.4 ng/mL

Reference intervals have not been formally verified in-house for pediatric patients. The published literature indicates that reference intervals for adult and pediatric patients are comparable.

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.

 

Reference intervals have not been formally verified in-house for pediatric patients. The published literature indicates that reference intervals for adult and pediatric patients are comparable.

Day(s) and Time(s) Performed

Monday through Friday; 5 a.m.-12 a.m., Saturday; 6 a.m.-6 p.m.

Analytic Time

Same day/1 day

Specimen Retention Time

3 months

Test Classification

This test has been cleared or approved by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information

84681

LOINC Code Information

Test ID Test Order Name Order LOINC Value
CPR C-Peptide, S 1986-9

 

Result ID Test Result Name Result LOINC Value
CRPN C-Peptide, S 1986-9

Forms

If not ordering electronically, complete, print, and send a General Request form (T239) with the specimen (http://www.mayomedicallaboratories.com/it-mmfiles/general-request-form.pdf).