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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 evaluate how well your pancreas makes insulin and can support diabetes management."]

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

Key facts at a glance

LOINC
13037-7
Short code
C peptide p fast SerPl-mCnc
Synonyms
C peptide p fast SerPl-mCnc
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 This Test Is Done

Doctors may order a C-peptide test to check if your pancreas is producing enough insulin. It’s often used to diagnose or monitor conditions like type 1 or type 2 diabetes, insulinoma (a rare tumor), or to assess how well insulin therapy is working. It can also help distinguish between insulin-dependent and insulin-independent diabetes.

What to Expect Before the Test

No special preparation is usually needed. You may be asked to fast for 8–12 hours before the test if it’s part of a fasting glucose study, but this isn’t always required. Bring any medications you’re taking to your doctor’s office.

How the Test Works

A blood sample is taken from a vein in your arm. The lab measures the C-peptide level in your serum or plasma using an immunoassay method, which detects the protein fragment released when insulin is produced.

What the Results Mean

Your results will be compared to a reference range provided by your healthcare provider. Low levels may suggest your pancreas isn’t producing enough insulin, while high levels could indicate overproduction (e.g., from a tumor). Normal levels help confirm your body’s natural insulin production.

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.

Clinical Significance

Short name

C-peptide level

Frequently asked questions

How does C-peptide differ from insulin levels?
C-peptide is a marker of endogenous insulin production and isn’t affected by insulin therapy. Unlike insulin, it’s not influenced by external insulin injections or oral medications, making it a more accurate measure of your natural pancreas function.
What if my C-peptide level is low?
A low C-peptide level may indicate type 1 diabetes (autoimmune destruction of pancreatic cells) or severe insulin deficiency. Your doctor may recommend further testing, like glucose tolerance or insulin sensitivity assessments, to guide treatment.
Can C-peptide test results change with diet or exercise?
C-peptide levels are generally stable unless your pancreas’s function is directly affected by conditions like diabetes, inflammation, or medications. Diet or exercise may influence blood sugar levels but not C-peptide itself unless they impact insulin production long-term.
  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