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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 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
38424-8
Short code
C peptide 2h p chal SerPl-sCnc
Synonyms
C peptide 2h 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

Doctors may order a C-peptide test to evaluate your pancreas’s ability to produce insulin. It’s often used in diagnosing diabetes, checking for insulin-producing tumors, or assessing how well insulin therapy is working. This test can also help distinguish between types of diabetes or other conditions affecting insulin production.

What to Expect Before the Test

No special preparation is needed for this blood test. You may be asked to fast for 8–12 hours before the draw, but this depends on your doctor’s instructions. Wear a comfortable shirt for easy access to your arm.

How the Test Is Performed

A healthcare provider will insert a needle into a vein in your arm to draw a small amount of blood. The sample is sent to a lab for analysis using a sensitive immunoassay method to measure C-peptide levels accurately.

What the Results Mean

Your results will show the concentration of C-peptide in your blood. High levels may indicate overproduction of insulin, while low levels could suggest insufficient pancreatic function. Your doctor will interpret these results in the context of your overall health and symptoms.

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

What does a high C-peptide level mean?
A high C-peptide level may suggest your body is producing extra insulin, which could be due to conditions like insulinoma (a tumor producing excess insulin) or certain metabolic disorders. It may also indicate overuse of insulin therapy if you have diabetes.
What does a low C-peptide level mean?
Low C-peptide levels often point to insufficient insulin production, which is common in Type 1 diabetes or severe pancreatic damage. It can also appear in cases of severe malnutrition or certain genetic disorders affecting insulin synthesis.
Can C-peptide test results change over time?
Yes, C-peptide levels can fluctuate based on factors like diet, stress, illness, or changes in medication. If your doctor orders this test repeatedly, they’ll track trends to understand how your pancreas is functioning over time.
  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