C-peptide (Serum or Plasma, Mass Concentration)
C-peptide is a small protein produced when your body makes insulin. This test measures its amount in your blood to help assess how well your pancreas is producing insulin naturally.
["This test helps evaluate insulin production and diabetes management."]
Key facts at a glance
- LOINC
- 27408-4
- Short code
- C peptide 20M p chal SerPl-mCnc
- Synonyms
- C peptide 20M p chal SerPl-mCnc
- Category
- coagulation
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 0.8
- Ref high
- 1.2
- Critical range
- — – 5 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 85610
- SNOMED
- 396252006
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
Why is this test done?
Your healthcare provider may order a C-peptide test to check if your pancreas is making enough insulin on its own. It can also help diagnose or monitor conditions like type 1 or type 2 diabetes, insulinoma (a rare tumor that causes high insulin levels), or to assess how well insulin therapy is working. Sometimes, it’s used alongside other tests to distinguish between insulin-dependent and insulin-independent diabetes.
What does the test involve?
A blood sample is taken from a vein, usually in your arm. The sample is sent to a lab where it is analyzed using a specialized immunoassay method to measure the C-peptide concentration. The test is typically done on serum or plasma.
What to expect before the test
No special preparation is usually needed, but you may be asked to fast for a few hours before the test if it’s part of a glucose tolerance test. Always follow your healthcare provider’s instructions. Avoid smoking or drinking alcohol before the test, as it may affect results.
What to expect during the test
The test itself is quick and painless. You may feel a slight pinch or sting when the needle is inserted. Afterward, you can resume normal activities immediately.
Reference range
INR: 0.8-1.2 (warfarin: 2.0-3.0)N/A
Inform your healthcare provider if you are taking blood thinners. No special preparation required.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
C-peptide levels help determine whether your diabetes is insulin-dependent or insulin-independent. High levels may indicate an insulin-producing tumor or overproduction of insulin, while low levels suggest insufficient insulin production. Monitoring C-peptide can also help tailor diabetes treatment plans, such as adjusting insulin doses or managing hypoglycemia (low blood sugar).
Short name
C-peptide level
Frequently asked questions
How does C-peptide differ from insulin?
Can C-peptide test results be affected by medications?
What if my C-peptide levels are abnormal?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy