Insulin, Fasting — Serum/Plasma, Substance Concentration
Measures insulin in a fasting blood sample to help evaluate insulin production, insulin resistance, and unexplained changes in blood glucose.
["Fasting insulin shows how much insulin your body is producing at rest and is most useful when interpreted with a glucose level."]
Key facts at a glance
- LOINC
- 59179-2
- Short code
- Insulin p fast SerPl-sCnc
- Synonyms
- Insulin p fast SerPl-sCnc
- Category
- hormone
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 10
- Ref high
- 40
- Critical range
- — – 500 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 84484
- SNOMED
- 302774002
- 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 fasting insulin test measures the amount of insulin in a blood sample drawn after you have not eaten. Insulin is a hormone made by the pancreas that helps glucose enter cells for energy.
Why might I need this test?
Your clinician may order this test to investigate insulin resistance, diabetes risk, unusual blood glucose results, or symptoms of low blood glucose. It is usually interpreted together with a simultaneous fasting glucose test and your medical history.
How is the test performed?
A blood sample is collected and the insulin level is measured in the serum or plasma portion of the sample. The laboratory commonly uses an immunoassay, although the exact method may vary.
How do I prepare for the test?
Follow your clinician's fasting instructions and do not eat or drink anything except water for the specified period. Taking medicines, supplements, or eating can affect the result, so tell the healthcare team about anything that may have influenced the test.
Reference range
Adult: 10-40 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.
A higher-than-expected fasting insulin level, especially when glucose is also elevated, may suggest that the body is resisting insulin's effects. A low insulin level can occur with excess insulin production, certain medicines, or pancreatic conditions, but one result alone does not establish a diagnosis. Insulin levels must be interpreted with glucose results, symptoms, medications, and other clinical findings.
Short name
Fasting Insulin
Frequently asked questions
Is fasting insulin the same as an insulin tolerance test?
Why is my insulin result checked with glucose?
Can medicines or illness affect the result?
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 17, 2026. · Read our editorial policy