Serum/plasma free cortisol concentration (mass concentration)
This test measures the amount of free cortisol, a form of the hormone cortisol that is not bound to proteins in your blood. Cortisol is involved in regulating metabolism, immune response, and stress reactions.
["Assessing free cortisol helps diagnose conditions like Cushing’s syndrome or adrenal insufficiency."]
Key facts at a glance
- LOINC
- 47922-0
- Short code
- GH 45M p Orn SerPl-aCnc
- Synonyms
- GH 45M p Orn SerPl-aCnc
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 0
- Ref high
- 17
- 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 Is Done
Your doctor may order this test if they suspect an issue with your adrenal glands, pituitary gland, or stress response. Free cortisol levels can help identify whether you have too much or too little cortisol in your body, which can cause various health problems, including weight changes, fatigue, or unusual mood swings.
What to Expect Before the Test
No special preparation is usually needed. You may be asked to fast for 8–12 hours before the test if your blood is drawn early in the morning, as cortisol levels naturally rise in the morning. If you’re taking medications that affect cortisol, let your healthcare provider know.
What Happens During the Test
A healthcare professional will draw blood from a vein in your arm. The sample is then sent to a lab for analysis. Free cortisol is measured using a sensitive immunoassay method to detect its presence in your serum or plasma.
What the Results Mean
Results are compared to reference ranges for free cortisol, which can vary slightly by lab. High levels may indicate conditions like Cushing’s syndrome, while low levels could suggest adrenal insufficiency or other hormonal imbalances. Your doctor will interpret results in the context of your symptoms and medical history.
Reference range
NCBI: NSE 0-17 ng/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.
Free cortisol testing is critical for diagnosing conditions that affect the body’s stress response and hormone regulation. Elevated levels may signal overproduction of cortisol due to tumors, excess steroid use, or certain cancers. Low levels can point to adrenal gland dysfunction, pituitary disorders, or long-term stress that has depleted cortisol reserves.
Short name
Free Cortisol
Frequently asked questions
How long does it take to get my results?
Can I take my medications before this test?
Is there anything I should avoid before this 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 17, 2026. · Read our editorial policy