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C-peptide (Serum or Plasma) with High-Performance Liquid Chromatography (HPLC) Measurement

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

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

Quick summary

["C-peptide helps doctors evaluate your pancreas’s insulin production and diagnose diabetes or other endocrine conditions."]

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

Key facts at a glance

LOINC
58518-2
Short code
C peptide 5h p Glc SerPl-mCnc
Synonyms
C peptide 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 This Test Is Done

Your doctor may order a C-peptide test to check if your pancreas is producing enough insulin. It can help diagnose type 1 or type 2 diabetes, rule out insulin resistance, or assess how well insulin therapy is working. It’s also used to monitor conditions like pancreatic cancer or other endocrine disorders.

How the Test Works

A blood sample is taken from a vein in your arm. The sample is sent to a lab where it’s analyzed using high-performance liquid chromatography (HPLC) to measure the concentration of C-peptide in your serum or plasma.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the test if instructed by your doctor. Wear comfortable clothing and plan to stay near the testing site for a short time.

What to Expect During the Test

A healthcare professional will insert a small needle into your vein to draw blood. You may feel a slight pinch, but the process is quick. You can sit or lie down during the procedure.

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 test

Frequently asked questions

What does a C-peptide test measure?
It measures the concentration of C-peptide, a protein produced in equal amounts with insulin during digestion. This helps assess your pancreas’s natural insulin production.
Can fasting affect C-peptide results?
Yes, fasting can influence C-peptide levels since insulin production is tied to glucose metabolism. If your doctor recommends fasting, follow their instructions to avoid misleading results.
Is C-peptide testing the same as checking insulin levels?
No, C-peptide is a marker of natural insulin production, while insulin levels can be affected by external factors like medications or stress. C-peptide is often preferred for more accurate diabetes assessment.
  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