Cortisol, Free (Serum)
This test measures the amount of free (unbound) cortisol in your blood. Cortisol is a hormone produced by your adrenal glands that helps regulate metabolism, immune response, and stress reactions.
["Free cortisol levels help assess adrenal function and potential hormone imbalances."]
Key facts at a glance
- LOINC
- 26828-4
- Short code
- Cortis Sal-aCnc
- Synonyms
- Cortis Sal-aCnc
- 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 Is This Test Done?
Your healthcare provider may order a free cortisol test to diagnose conditions like Cushing’s syndrome (overactive adrenal glands), adrenal insufficiency (underactive adrenal glands), or to evaluate stress-related hormone changes. It can also help monitor treatment for these conditions.
What to Expect During the Test
A blood sample will be taken from a vein in your arm. You may feel a slight pinch, but it usually doesn’t cause discomfort. The sample is collected in a sterile tube and sent to the lab for analysis.
Sample Preparation and Storage
The blood sample is typically processed immediately or stored under cold conditions to preserve cortisol levels. Free cortisol is measured directly in serum, so no special preparation is needed beyond fasting if instructed (though fasting isn’t always required for this test).
What the Results Mean
Results are interpreted in the context of your clinical symptoms, medical history, and other tests. Elevated levels may indicate overproduction of cortisol, while low levels may suggest adrenal gland dysfunction. Your doctor will discuss findings with you.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance: Free cortisol testing is critical for diagnosing hormonal imbalances that affect metabolism, stress tolerance, and immune function. It helps differentiate between conditions like primary adrenal insufficiency (Addison’s disease) and secondary adrenal insufficiency, as well as conditions like Cushing’s syndrome or ectopic ACTH syndrome.
Short name
Free Cortisol
Frequently asked questions
What causes abnormal free cortisol levels?
How often should this test be repeated?
Can diet or lifestyle affect cortisol levels?
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