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C-peptide (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 diagnose diabetes and check insulin production levels."]

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

Key facts at a glance

LOINC
57894-8
Short code
C peptide 100M p chal SerPl-sCnc
Synonyms
C peptide 100M 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 Is This Test Done?

Your doctor may order a C-peptide test to evaluate whether your diabetes is caused by insufficient insulin production (type 1 diabetes) or insulin resistance (type 2 diabetes). It can also help monitor insulin levels in people with known diabetes or those taking insulin therapy.

What Does the Test Involve?

A blood sample is taken from a vein, usually in your arm. The sample is sent to a lab for analysis. The test measures the concentration of C-peptide in your serum or plasma.

What to Expect Before the Test

No special preparation is needed for this test. However, if you’re on insulin or certain medications, let your healthcare provider know before the test.

What to Expect After the Test

You may feel slight discomfort or bruising at the injection site. The blood sample is usually processed within hours, and results are ready within a few days.

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 Low C-peptide Level Mean?
A low C-peptide level often suggests type 1 diabetes, where the pancreas produces little to no insulin. It may also indicate severe insulin resistance or other pancreatic disorders.
What Does a High C-peptide Level Mean?
High C-peptide levels can indicate type 2 diabetes with adequate insulin production but impaired function. It may also be seen in people with obesity or metabolic syndrome.
Can C-peptide levels change with diet or exercise?
Yes, lifestyle factors like diet and exercise can influence insulin and C-peptide levels. However, C-peptide itself is not directly affected by diet, but changes in insulin production may indirectly reflect metabolic health.
  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