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Peptide fragment analysis of proinsulin (specifically measuring C-peptide)

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

This test measures the C-peptide, a small protein fragment produced along with insulin during blood sugar regulation. It helps assess whether your pancreas is producing insulin naturally.

Quick summary

["C-peptide helps confirm natural insulin production and diagnose diabetes or pancreatic issues."]

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

Key facts at a glance

LOINC
108141-3
Short code
C peptide sp5 SerPl-mCnc
Synonyms
C peptide sp5 SerPl-mCnc
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 This Test Is Done

Doctors may order a C-peptide test to evaluate how well your pancreas is working to produce insulin. It’s often used to distinguish between types of diabetes, check for insulin-producing tumors, or monitor conditions like autoimmune diabetes or pancreatic diseases.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the draw. Bring your medical records if you have diabetes or a history of pancreatic issues.

How the Test Works

A blood sample is taken from a vein in your arm. The lab analyzes the C-peptide level in your serum or plasma to determine insulin production status.

Possible Results and Their Meaning

Low C-peptide levels may indicate insufficient insulin production (e.g., type 1 diabetes or pancreatic damage). High levels could suggest overproduction (e.g., insulinoma). Normal levels confirm natural insulin secretion.

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 causes abnormal C-peptide levels?
Abnormally low C-peptide levels can result from type 1 diabetes, severe pancreatic inflammation, or genetic disorders impairing insulin synthesis. Abnormally high levels may signal insulin-secreting tumors or rare metabolic conditions.
Can diet or fasting affect C-peptide results?
Fasting for 8–12 hours before testing helps ensure accurate results, as food can temporarily alter insulin and C-peptide levels. However, extreme dietary changes (e.g., very low-carb diets) may still influence outcomes.
Is C-peptide testing painful?
The blood draw is mild discomfort for a few seconds, similar to a routine blood test. Most people tolerate it well, and you can resume normal activities afterward.
  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