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C-peptide (Serum or Plasma, Quantitative)

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 assess insulin production and diagnose diabetes or pancreatic issues."]

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

Key facts at a glance

LOINC
38421-4
Short code
C peptide 30M p chal SerPl-sCnc
Synonyms
C peptide 30M 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 how well your pancreas produces insulin. It can help diagnose type 1 or type 2 diabetes, rule out insulin overproduction (hyperinsulinism), or check for pancreatic diseases. It’s also used before and after pancreatic surgery to monitor insulin production.

How the Test Works

A small blood sample is taken from a vein, usually in your arm. The sample is sent to a lab, where it’s analyzed using an immunoassay method to measure C-peptide levels in your blood.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for a few hours before the test if it’s part of a glucose tolerance test. Wear comfortable clothing and bring any medications you’re currently taking.

What the Results Mean

Results help doctors understand insulin production. High levels may indicate insulin-producing tumors or overproduction, while low levels can suggest diabetes or pancreatic damage. Your doctor will interpret results in the context of your overall health.

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.

Clinical Significance

Short name

C-peptide level

Frequently asked questions

Why might my doctor ask for this test?
To diagnose diabetes (especially type 1), rule out insulin-related conditions, or assess pancreatic function before or after surgery. It’s also useful for monitoring chronic diseases like diabetes or pancreatic cancer.
What does a high or low C-peptide level usually mean?
High levels may signal excess insulin production (e.g., insulinoma) or overproduction from a tumor. Low levels often indicate diabetes, where the pancreas isn’t producing enough insulin. Your doctor will discuss findings with you.
Do I need to prepare differently if I’m pregnant?
Yes, pregnant women may need fasting or additional testing to ensure accurate results. Always follow your healthcare provider’s specific instructions for your situation.
  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