C-peptide (Serum or Plasma)
This test measures the amount of C-peptide, a small protein produced along with insulin when your pancreas releases it to regulate blood sugar.
["C-peptide helps confirm insulin production and diagnose diabetes or other pancreatic conditions."]
Key facts at a glance
- LOINC
- 47591-3
- Short code
- C peptide 3M p Glc SerPl-sCnc
- Synonyms
- C peptide 3M p Glc SerPl-sCnc
- Category
- glucose
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 0.8
- Ref high
- 1.2
- Critical range
- — – 5 N/A
- Fasting
- true
- 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 doctor may order a C-peptide test to evaluate how well your pancreas produces insulin. It can help diagnose type 1 or type 2 diabetes, rule out insulin resistance, or assess pancreatic function in people with unexplained high or low blood sugar levels. It may also be used to monitor insulin production in people with diabetes or those taking insulin therapy.
What Does the Test Measure?
C-peptide is a byproduct of insulin production. Unlike insulin, which circulates briefly and is cleared quickly from your blood, C-peptide remains in your bloodstream for a longer time. Measuring C-peptide helps doctors distinguish between insulin-dependent and insulin-independent causes of blood sugar changes.
Sample Collection and Preparation
A blood sample is taken from a vein in your arm. The sample is collected in a tube that may contain an anticoagulant to prevent clotting. The blood is then processed to separate the serum or plasma for testing. This test is typically done on fresh or stored serum/plasma.
What to Expect Before the Test
No special preparation is usually needed for a C-peptide test. However, if you are on insulin therapy, your doctor may advise you to stop taking insulin for a short period before the test to ensure accurate results.
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.
A C-peptide test is crucial for diagnosing diabetes and assessing pancreatic health. High levels may indicate overproduction of insulin (e.g., in insulinoma or pancreatic tumors), while low levels suggest insufficient insulin production (e.g., type 1 diabetes or pancreatic damage). It can also help differentiate between insulin-dependent and insulin-independent causes of hypoglycemia (low blood sugar).
Short name
C-peptide level
Frequently asked questions
What Are the Normal Results?
How Long Does It Take to Get Results?
Can I Eat or Drink Before This Test?
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