Free Insulin, Serum/Plasma — Mass Concentration
Measures the amount of unbound insulin in serum or plasma, which can help evaluate insulin production and the body's handling of glucose.
["Free insulin measures circulating insulin that is not bound to other substances and may be used in selected evaluations of glucose regulation."]
Key facts at a glance
- LOINC
- 43942-2
- Short code
- Insulin Free SerPl-mCnc
- Synonyms
- Insulin Free SerPl-mCnc
- 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 portion of insulin in the blood that is not bound to proteins. Insulin is a hormone made by the pancreas that helps move glucose into cells and helps regulate blood sugar.
Why might I need this test?
Free insulin may be ordered in selected situations to help assess how the body produces and responds to insulin. It is sometimes considered when evaluating unexplained changes in blood glucose, insulin resistance, or symptoms related to low blood sugar. It is often interpreted alongside glucose, fasting status, and other tests.
How is the test performed?
A blood sample is drawn from a vein and tested in a laboratory using an assay that measures free insulin in serum or plasma. The result is reported as a mass concentration, meaning the amount of insulin per unit volume of blood.
How do I prepare for the test?
Follow the instructions provided by your healthcare professional. The test is often performed after fasting for several hours, and your clinician should tell you whether food and drinks should be avoided beforehand. Do not stop 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.
◆Associated findings1
Short name
Free insulin
Frequently asked questions
Is fasting insulin the same as free insulin?
Why is free insulin measured separately from total insulin?
Does an abnormal free insulin result diagnose diabetes?
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