Cortisol, Free (Serum/Plasma)
This test measures the amount of free (unbound) cortisol, a hormone produced by your adrenal glands, in your blood. Free cortisol reflects your body’s current cortisol levels, which can help assess conditions like adrenal insufficiency or Cushing’s syndrome.
["Free cortisol helps diagnose hormonal imbalances affecting stress response and metabolism."]
Key facts at a glance
- LOINC
- 46403-2
- Short code
- Cortis 2h p Ins IV SerPl-mCnc
- Synonyms
- Cortis 2h p Ins IV 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 Is This Test Done?
Your doctor may order a free cortisol test to evaluate symptoms such as fatigue, weight changes, or unusual mood swings that could indicate adrenal gland issues. It’s also used to confirm or rule out conditions like Addison’s disease (adrenal insufficiency) or Cushing’s syndrome (excess cortisol).
What to Expect Before the Test
No special preparation is needed, but you may be asked to fast for 8–12 hours before the test if it’s part of a 24-hour urine collection. Bring any medications you’re taking, as some may affect results.
How the Test Is Done
A healthcare provider will draw blood from a vein in your arm. The blood sample is 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 signal underlying hormonal disorders that require further medical evaluation.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance: Free cortisol is critical for regulating stress responses, immune function, and metabolism. Chronic low levels may lead to fatigue, salt cravings, or hypotension, while elevated levels can cause weight gain, muscle weakness, or high blood pressure. This test helps guide treatment for conditions like adrenal insufficiency or hypercortisolism.
Short name
Free Cortisol
Frequently asked questions
What causes abnormal free cortisol levels?
How long does it take to get results?
Can diet or medications affect 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 16, 2026. · Read our editorial policy