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Insulin, Proinsulin, and C-Peptide, Serum/Plasma — Substance Concentration

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

Measures insulin, proinsulin, and C-peptide in blood to assess pancreatic insulin production and help evaluate diabetes and related disorders.

Quick summary

["These blood markers show how the pancreas produces and processes insulin."]

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

Key facts at a glance

LOINC
51427-3
Short code
Insulin pre/p chal SerPl-sCnc
Synonyms
Insulin pre/p chal SerPl-sCnc
Category
hormone
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
2.6
Ref high
24.9
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
83525
SNOMED
413618004
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

What is this test?

This blood test measures insulin and two related substances: proinsulin, an inactive form of insulin, and C-peptide, a protein released when insulin is made. Together, they provide information about how the pancreas produces and processes insulin.

Why might I need this test?

The test may be used to help diagnose or monitor diabetes, evaluate symptoms of low blood sugar, or assess pancreatic function. It can also help distinguish low insulin levels caused by reduced pancreatic production from low levels caused by insulin injected for treatment.

How is the test performed?

A blood sample is drawn from a vein and analyzed in the laboratory, usually using immunoassay methods. Your blood glucose and current diabetes medications are also considered when interpreting the results.

How do I prepare for the test?

Follow the preparation instructions provided by your healthcare professional; fasting may be required. The timing of the blood draw is important, especially if you take insulin, so do not change or delay medications without medical guidance.

Reference range

Fasting: 2.6-24.9 μIU/mLN/A

Specimen: serum

No special preparation usually required. Stay well hydrated. Inform your healthcare provider of all medications and supplements you are taking.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Insulin, proinsulin, and C-peptide

Frequently asked questions

What does C-peptide measure?
C-peptide is released into the bloodstream when the pancreas makes insulin. Its level helps show the body's own insulin production, including when a person receives injected insulin.
Why are proinsulin and insulin measured together?
Proinsulin is a precursor that must be processed into active insulin. Measuring both can help evaluate how the pancreas creates and processes insulin.
Do I need to fast before this test?
Fasting may be required, depending on the laboratory and the reason for testing. Ask your healthcare professional about fasting and medication timing, and never stop prescribed insulin without medical advice.
  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