Insulin, Free and Total, Serum/Plasma — Concentration
Measures free insulin and total insulin in blood. It may help evaluate insulin production, insulin resistance, and unexplained low blood sugar.
["This blood test shows how much insulin is freely available and how much is present in total."]
Key facts at a glance
- LOINC
- 48615-9
- Short code
- Insulin.free+total Pnl SerPl-aCnc
- Synonyms
- Insulin.free+total Pnl SerPl-aCnc
- Category
- hormone
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 44
- Ref high
- 147
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 84075
- SNOMED
- 27550007
- 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 test measures two forms of insulin in serum or plasma. Free insulin is not bound to other substances, while total insulin includes both free insulin and insulin bound to proteins.
Why might I need this test?
A clinician may order this test when evaluating insulin resistance, diabetes treatment, unexplained low blood sugar, or how well the pancreas is producing insulin. It may be used with other tests such as glucose and C-peptide.
How is the test performed?
A blood sample is collected and analyzed in a laboratory. The laboratory reports the concentrations of free insulin and total insulin, sometimes as part of a broader insulin panel.
How do I prepare for the test?
Follow your clinician's instructions. Fasting for several hours may be required, and the timing of the blood draw is important because insulin levels change throughout the day. Continue prescribed medicines unless your clinician tells you otherwise.
Reference range
Adult: 44-147 U/LN/A
No special preparation required. Avoid fatty meals before the test if possible.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
High insulin levels can occur with insulin resistance or when the body is producing more insulin than the tissues can use. Low insulin levels may suggest reduced insulin production or the use of insulin or certain diabetes medicines. Results must be interpreted with glucose, symptoms, medicines, and other laboratory tests.
Short name
Free and total insulin
Frequently asked questions
What is the difference between free and total insulin?
Does this test diagnose diabetes?
Why can the timing of the blood sample matter?
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