Test Details
Methodology
Electrochemiluminescence immunoassay (ECLIA)
Result Turnaround Time
2 - 4 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Use
Urine C-peptide is measured when a continuous assessment of β-cell function is desired or frequent blood sampling is not practical (eg, in children).1 C-peptide excretion in urine has been used to assess pancreatic function in gestational diabetes and in patients with unstable glycemic control in insulin-dependent diabetes mellitus (IDDM).2,3
Special Instructions
This test may exhibit interference when sample is collected from a person who is consuming a supplement with a high dose of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R). It is recommended to ask all patients who may be indicated for this test about biotin supplementation. Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.
Custom Additional Information
C-peptide is a single-chain 31-amino acid (AA 33-63) connecting (C) polypeptide with a molecular weight of approximately 3021 daltons.1,5 In the process of biosynthesis of insulin, the C-peptide is formed as a byproduct together with insulin by the proteolytic cleavage of the precursor molecule proinsulin, stored in secretory granules in the Golgi complex of the pancreatic β-cells. Proinsulin, in turn, was cleaved from preproinsulin.1,6
C-peptide fulfills an important function in the assembly of the two-chain insulin (α- and β-chain) structure and the formation of the two disulfide bonds within the proinsulin molecule. Insulin and C-peptide are secreted in equimolar amounts and released into circulation via the portal vein.2 As half of the insulin, but almost none of the C-peptide, is extracted in the liver, C-peptide has a longer half-life (about 35 minutes) than insulin; 5 to 10 times higher concentration of C-peptide persists in the peripheral circulation, and these levels fluctuate less than insulin.1,2,6
The liver does not extract C-peptide, which is removed from the circulation by the kidneys and degraded, with a fraction excreted unchanged in the urine. The concentration in urine is about 20- to 50-fold higher than in serum. C-peptide concentrations are, therefore, elevated in renal disease.1,5,6
Specimen Requirements
Specimen
Urine (24-hour), frozen
Volume
10 mL
Minimum Volume
1 mL (Note: This volume does not allow for repeat testing.)
Container
Plastic urine container
Collection Instructions
Instruct the patient to void at 8 AM and discard the specimen. Then collect all urine including the final specimen voided at the end of the 24-hour collection period (ie, 8 AM the next morning) in a 24-hour urine collection container. pH should be 4 to 7.
Stability Requirements
Temperature | Period |
|---|---|
Room temperature | 1 day |
Refrigerated | 14 days |
Frozen | 14 days |
Freeze/thaw cycles | Stable x3 |
Reference Range
17.2−181.0 μg/24 hours
Storage Instructions
Freeze
Causes for Rejection
pH <3 or pH >8
Footnotes
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 003236 | C-Peptide, Urine | 1987-7 | 003237 | C-Peptide, Urine | ng/mL | 1987-7 |
| 003236 | C-Peptide, Urine | 1987-7 | 003238 | C-Peptide,Urine 24hr | ug/24 hr | 27944-8 |
| Order Code | 003236 | |||||
| Order Code Name | C-Peptide, Urine | |||||
| Order Loinc | 1987-7 | |||||
| Result Code | 003237 | |||||
| Result Code Name | C-Peptide, Urine | |||||
| UofM | ng/mL | |||||
| Result LOINC | 1987-7 | |||||
| Order Code | 003236 | |||||
| Order Code Name | C-Peptide, Urine | |||||
| Order Loinc | 1987-7 | |||||
| Result Code | 003238 | |||||
| Result Code Name | C-Peptide,Urine 24hr | |||||
| UofM | ug/24 hr | |||||
| Result LOINC | 27944-8 |