Cortisol, Free (Serum or Plasma)
This test measures the amount of free cortisol, a form of the hormone cortisol that circulates freely in your blood. Free cortisol is important for regulating stress responses, metabolism, and immune function.
["Free cortisol helps your body manage stress and maintain balance in key bodily functions."]
Key facts at a glance
- LOINC
- 43217-9
- Short code
- Cortis 15M p ACTH IM SerPl-mCnc
- Synonyms
- Cortis 15M p ACTH IM SerPl-mCnc
- Category
- hormone
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 10
- Ref high
- 60
- 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 check for conditions like Cushing’s syndrome (overactive adrenal glands), adrenal insufficiency (underactive adrenal glands), or to evaluate how your body responds to stress or medications that affect cortisol levels.
What to Expect Before the Test
No special preparation is usually needed, but if your test involves a blood draw, you may want to avoid caffeine or alcohol for a few hours beforehand. If this is a 24-hour urine test (not applicable here), you would collect urine samples over a full day.
What Happens During the Test?
A healthcare provider will take a blood sample from a vein in your arm. The sample is then sent to a lab to measure free cortisol levels using a sensitive immunoassay method.
What Are the Results?
Results are typically reported as a concentration value (in micrograms per deciliter or nanograms per deciliter). Your results will be compared to reference ranges provided by your lab or doctor.
Reference range
NCBI: ACTH 10-60 pg/mLN/A
Typically collected in the morning (8-10 AM). Inform your provider if taking steroid medications.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Free cortisol levels can indicate whether your adrenal glands are producing too much or too little cortisol. Abnormal results may signal conditions affecting your stress response, metabolism, or immune system. Your doctor will interpret results in the context of your symptoms and medical history.
Short name
Free Cortisol
Frequently asked questions
What does a high free cortisol level mean?
What does a low free cortisol level mean?
How often should I get 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