Cortisol, Free (Serum or Plasma)
This test measures the amount of free cortisol, a hormone produced by your adrenal glands, in your blood. Free cortisol is the active form that circulates freely in your bloodstream and is important for managing stress, immune response, and metabolism.
["Free cortisol helps assess adrenal gland function and potential hormone imbalances."]
Key facts at a glance
- LOINC
- 16670-2
- Short code
- Cortis 15M p chal SerPl-mCnc
- Synonyms
- Cortis 15M p chal SerPl-mCnc
- Category
- hormone
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- 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
Why This Test Might Be Ordered
Your healthcare provider may recommend a free cortisol test if you have symptoms like unexplained weight changes, fatigue, muscle weakness, or signs of adrenal insufficiency or hyperadrenalism (such as high blood pressure, mood changes, or unusual thirst). It may also be used to diagnose conditions like Cushing’s syndrome or Addison’s disease.
What to Expect Before the Test
No special preparation is usually needed. You may be asked to fast for 8 hours before the test, but this is not always required. Bring any medications you’re currently taking, as they could affect results.
How the Test Is Performed
A blood sample will be drawn from a vein in your arm. The sample is then sent to a lab for analysis using a sensitive immunoassay method to measure free cortisol levels.
What the Results Mean
Results are compared to reference ranges specific to your age, sex, and health status. Abnormally high or low levels may indicate hormonal imbalances or underlying medical conditions that need further evaluation.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Free cortisol levels help diagnose conditions like adrenal insufficiency (Addison’s disease), Cushing’s syndrome, or other hormonal disorders. Chronic stress, certain medications, or liver/kidney disease can also affect cortisol levels, so results should be interpreted in the context of your overall health and symptoms.
Short name
Free Cortisol
Frequently asked questions
What causes abnormal cortisol levels?
How long does it take to get results?
Can I take my medications before the test?
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