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C-peptide (Serum or Plasma) Concentration

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of C-peptide, a small protein produced along with insulin when your pancreas releases it to regulate blood sugar.

Quick summary

["C-peptide helps doctors assess how well your pancreas is producing insulin naturally."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
77652-6
Short code
C peptide 5h p chal SerPl-sCnc
Synonyms
C peptide 5h p chal SerPl-sCnc
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 This Test Is Done

Your doctor may order a C-peptide test to evaluate your pancreas’s function, especially if you have diabetes or suspect it may not be producing enough insulin. It can also help distinguish between types of diabetes or insulin dependence.

What to Expect Before the Test

No special preparation is needed. You’ll provide a blood sample, usually drawn from a vein in your arm. If you’re on insulin, your doctor may advise timing your dose to avoid interference with results.

What the Results Mean

Higher-than-normal levels may indicate overproduction of insulin, while lower-than-normal levels could suggest diabetes or reduced pancreatic function. Results are interpreted in the context of your medical history and symptoms.

Common Conditions Linked to C-peptide Testing

This test is often used to diagnose or monitor diabetes, rule out insulin overproduction (e.g., insulinoma), or assess pancreatic health in conditions like pancreatitis or autoimmune disorders.

Reference range

INR: 0.8-1.2 (warfarin: 2.0-3.0)N/A

Specimen: serum

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.

◆Associated findings1

Short name

C-peptide level

Frequently asked questions

How does C-peptide differ from insulin levels?
Unlike insulin, C-peptide is not affected by insulin injections or certain medications, making it a more accurate measure of natural insulin production.
What if my C-peptide results are abnormal?
Abnormal results may prompt further testing (e.g., glucose tolerance or oral glucose challenge) or adjustments to your diabetes management plan, depending on your symptoms and medical history.
Can diet or fasting affect C-peptide results?
Fasting may slightly alter C-peptide levels, so your doctor may recommend fasting or non-fasting testing based on your clinical needs. Avoiding alcohol or strenuous activity before the test can also improve accuracy.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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