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C-peptide (Serum/Plasma) with High-Performance Liquid Chromatography (HPLC) Quantification

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

This test measures C-peptide, a small protein produced equally with insulin during digestion, helping 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
58516-6
Short code
C peptide 4h p Glc SerPl-mCnc
Synonyms
C peptide 4h 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 how well your pancreas produces insulin. It’s often used in diagnosing diabetes, checking insulin dependence, or monitoring treatment in people with diabetes or suspected insulin misuse (e.g., insulin pumps or injections). It can also help assess pancreatic health in conditions like pancreatitis or cystic fibrosis.

What Does the Test Measure?

C-peptide is released into the bloodstream at the same time as insulin. Unlike insulin, which is broken down quickly, C-peptide remains stable in the blood. Measuring it helps determine if your body is producing insulin naturally or if external sources are needed.

Sample Collection and Preparation

A blood sample is drawn from a vein in your arm. The sample is sent to a lab for analysis using high-performance liquid chromatography (HPLC), a precise method to measure C-peptide levels accurately.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the test if your doctor directs it. Avoid smoking or consuming alcohol for a few hours before the draw, as these can affect blood chemistry.

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

How can my C-peptide results affect my health?
Low C-peptide levels may indicate insulin deficiency, often seen in type 1 diabetes or severe type 2 diabetes. High levels could suggest overproduction of insulin (e.g., from a tumor) or insulin resistance. Your doctor will use these results alongside other tests to guide treatment, such as insulin therapy or lifestyle changes.
What if my C-peptide test is abnormal?
If your results are outside expected ranges, your doctor will discuss them with you. Abnormal levels may point to underlying conditions like diabetes, pancreatic issues, or other metabolic disorders. Follow-up tests or additional questions may be needed to understand the cause and plan the best care.
Can diet or medications affect my C-peptide test?
Yes, certain foods (like high-protein meals) and medications (e.g., some diabetes drugs) can temporarily influence C-peptide levels. Your doctor may recommend specific timing or adjustments to ensure accurate results. Always follow their instructions for the best interpretation of your test.
  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