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C-peptide (Serum/Plasma) Concentration

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

This test measures the amount of C-peptide, a natural substance produced by your pancreas along with insulin, to help assess insulin production and function.

Quick summary

["C-peptide helps distinguish between natural insulin production and external insulin use."]

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

Key facts at a glance

LOINC
57650-4
Short code
C peptide 70M pre chal SerPl-sCnc
Synonyms
C peptide 70M pre 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 Is This Test Done?

Your doctor may order a C-peptide test to check how well your pancreas produces insulin. It can help diagnose diabetes, monitor diabetes treatment, or evaluate conditions like insulinoma (a rare tumor that causes excessive insulin production).

What Does It Measure?

C-peptide is a small protein released by your pancreas in equal amounts with insulin. Unlike insulin, C-peptide is not influenced by insulin injections or oral diabetes medications, making it useful for assessing natural insulin production.

How Is the Test Performed?

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

What Are Common Uses?

C-peptide testing is often used to confirm diabetes diagnosis, evaluate insulin resistance, and monitor the effectiveness of diabetes treatments. It can also help identify whether insulin production is normal or impaired.

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: C-peptide levels provide critical insights into pancreatic function. Low levels may indicate insufficient insulin production, while high levels could suggest overproduction (e.g., insulinoma). Normal levels help confirm healthy insulin secretion, aiding in diabetes management and ruling out other conditions.

Short name

C-peptide level

Frequently asked questions

What does a C-peptide test tell me about my diabetes?
A C-peptide test helps determine whether your diabetes is caused by insufficient insulin production (type 1 diabetes) or insulin resistance (type 2 diabetes). If your levels are low, it may suggest type 1 diabetes or poor insulin secretion. If levels are normal, it supports a diagnosis of type 2 diabetes or other causes.
How does C-peptide differ from insulin levels?
C-peptide is naturally produced by your pancreas with insulin, so it reflects your body’s own insulin production. Insulin levels can be artificially elevated by medications or injections, whereas C-peptide is unaffected by these factors, making it a more reliable marker of natural insulin function.
Can C-peptide test results change with diet or exercise?
C-peptide levels are primarily influenced by your pancreas’s insulin production and are not significantly affected by short-term diet or exercise. However, chronic lifestyle factors like diet and activity can impact overall insulin sensitivity and diabetes management 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