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C-peptide measured by high-performance liquid chromatography (HPLC) in serum/plasma

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

This test measures C-peptide, a small protein produced equally with insulin during digestion. It helps assess how much insulin your pancreas naturally makes.

Quick summary

["C-peptide helps distinguish between insulin use and natural production for diabetes management."]

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

Key facts at a glance

LOINC
58505-9
Short code
C peptide 2.5h p Glc SerPl-mCnc
Synonyms
C peptide 2.5h p Glc SerPl-mCnc
Category
glucose
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
0.8
Ref high
1.2
Critical range
— – 5 N/A
Fasting
true
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 your pancreas’s ability to produce insulin. It’s often used in diagnosing type 1 diabetes, monitoring insulin-dependent conditions, or checking for insulin resistance or overproduction.

What Does the Test Involve?

A blood sample is taken from a vein, usually in your arm. The sample is sent to a lab where it’s analyzed using high-performance liquid chromatography (HPLC) to measure C-peptide levels.

What to Expect Before the Test

No special preparation is needed, but inform your doctor about any medications, including insulin, you’re taking. Avoid fasting unless instructed, as it may affect results.

What Are the Results Typically Used For?

High C-peptide levels may indicate your body produces insulin naturally, while low levels suggest insulin deficiency or dependence on external sources.

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 normal C-peptide level mean?
A normal C-peptide level doesn’t provide a single range—it reflects your body’s natural insulin production. Your doctor will interpret results in the context of your medical history and symptoms.
Does fasting affect C-peptide test results?
Yes, fasting can influence C-peptide levels. If your doctor hasn’t instructed otherwise, eat a normal meal before the test to get an accurate reading of your natural insulin production.
Can C-peptide test results change over time?
Yes, C-peptide levels can fluctuate due to changes in diet, stress, illness, or medication. Regular monitoring may be needed for conditions like diabetes or insulin-dependent disorders.
  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