Insulin, Free — Serum/Plasma, Substance Concentration
Measures the amount of insulin that is not bound to proteins in blood. It can help evaluate insulin production and the body’s handling of glucose.
["Free insulin measures circulating insulin that is available to act on the body’s cells."]
Key facts at a glance
- LOINC
- 25447-4
- Short code
- Insulin Free SerPl-sCnc
- Synonyms
- Insulin Free 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 free insulin, the fraction of insulin not attached to carrier proteins. It is different from a total insulin test, which includes both free and protein-bound insulin.
Why might I need this test?
Free insulin may be ordered when evaluating low or high blood sugar, insulin resistance, or how the body responds to meals and insulin therapy. It may also be used in the assessment of certain conditions affecting insulin levels.
How is the test performed?
A blood sample is collected, usually from a vein. The laboratory uses a specialized method to distinguish free insulin from insulin bound to proteins.
How do I prepare for the test?
Follow the preparation instructions provided by your healthcare professional. Fasting may be required in some situations, and the timing of the test can be important because insulin changes after eating. Do not stop insulin or other diabetes medicines unless your clinician instructs you to do so.
Reference range
Fasting: 2.6-24.9 μIU/mLN/A
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.
A free insulin result that does not match the expected level for the person’s blood glucose or clinical situation may suggest differences in insulin production, insulin resistance, or medication effects. Results should be interpreted with the related glucose tests, symptoms, medications, and medical history.
Short name
Free Insulin
Frequently asked questions
What is the difference between free and total insulin?
Does this test diagnose diabetes?
Why might insulin be measured after a meal?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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