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Peptide F (C-peptide) in Serum or Plasma

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

This test measures the amount of C-peptide, a natural byproduct of insulin production, in your blood. It helps assess how well your pancreas is producing insulin.

Quick summary

["C-peptide helps confirm insulin production and diagnose diabetes or other pancreatic conditions."]

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

Key facts at a glance

LOINC
42180-0
Short code
C peptide p fast SerPl-sCnc
Synonyms
C peptide p fast SerPl-sCnc
Category
coagulation
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
40
Critical range
— – 5 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84484
SNOMED
302774002
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 insulin production, diagnose type 1 or type 2 diabetes, or check for conditions like pancreatic cancer or insulinoma. It can also help distinguish between insulin-dependent and insulin-independent diabetes.

How Is the Test Performed?

A blood sample is taken from a vein, usually in your arm. The sample is sent to a lab for analysis using an immunoassay method to measure C-peptide levels.

What Do Results Mean?

Results are not provided with specific reference ranges, as they vary by lab. High levels may suggest overproduction of insulin, while low levels could indicate insufficient insulin production or pancreatic issues.

Common Conditions Monitored

C-peptide testing is often used to monitor diabetes management, rule out insulin misuse (e.g., in insulin-dependent diabetes), or assess pancreatic health in suspected tumors or autoimmune diseases.

Reference range

Adult: 10-40 U/LN/A

Specimen: serum

No special preparation required. Avoid fatty meals before the test if possible.

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 C-peptide test measure?
A C-peptide test measures the amount of C-peptide, a protein fragment produced naturally when insulin is created in the pancreas. It reflects your body’s own insulin production, not external insulin sources.
Why might my doctor order a C-peptide test?
Your doctor may order a C-peptide test to check if your diabetes is caused by insufficient insulin production (type 1 diabetes) or insulin resistance (type 2 diabetes), to evaluate pancreatic health, or to confirm suspected insulinomas (tumors that produce excess insulin).
Is fasting required for this test?
No fasting is typically required for a C-peptide test, as it measures natural insulin production without interference from recent food intake.
  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