Free Insulin, Serum/Plasma
Measures the amount of insulin not bound to proteins in blood. It may be used in selected cases to assess pancreatic insulin production.
["This blood test measures circulating free insulin, which is not bound to other proteins."]
Key facts at a glance
- LOINC
- 108829-3
- Short code
- Insulin Free Msmt SerPl
- Synonyms
- Insulin Free Msmt SerPl
- 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?
A free insulin test measures the part of insulin in serum or plasma that is not bound to proteins. Most routine insulin tests measure total insulin instead, so this test may require a specific laboratory order.
Why might I need this test?
Free insulin may be considered in selected evaluations of low blood sugar, suspected excess insulin production, or unusual insulin results. It is often interpreted with glucose, symptoms, medication use, and other pancreatic hormone tests.
How is the test performed?
A blood sample is collected, usually from a vein. The laboratory uses an immunoassay to measure free insulin in the serum or plasma sample.
How do I prepare for the test?
Follow the laboratory's instructions. Timing may matter, particularly if the test is being used to evaluate low blood sugar, so tell the care team about symptoms, recent meals, and insulin or diabetes medicines.
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.
An unexpectedly high free insulin result, especially when accompanied by low blood sugar, may suggest the body is producing too much insulin. A low result may occur with reduced pancreatic insulin production, high blood sugar, or the use of medicines that lower insulin. Results should be interpreted by a clinician because fasting status, laboratory methods, and other factors can affect them.
Short name
Free Insulin
Frequently asked questions
Is this the same as a routine insulin test?
Why is the timing of the blood sample important?
Does an abnormal result diagnose diabetes or an insulinoma?
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