Cortisol, Serum (Free)
This test measures the amount of free cortisol, a form of the hormone cortisol that circulates freely in your bloodstream, not bound to proteins.
["Free cortisol helps regulate stress responses and metabolism; abnormal levels may indicate adrenal gland issues or other conditions."]
Key facts at a glance
- LOINC
- 1447-2
- Short code
- Cortis pre 40 ug ACTH IM SerPl-mCnc
- Synonyms
- Cortis pre 40 ug 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 diagnose or monitor conditions like Cushing’s syndrome (overactive adrenal glands), adrenal insufficiency, or to evaluate stress-related hormone imbalances. It can also help assess pituitary gland function or rule out certain hormonal disorders.
What to Expect Before the Test
No special preparation is needed, but you may be asked to avoid certain medications (like steroids) that could affect cortisol levels. If you’re taking them, your doctor will guide you. Bring a list of your current medications to your appointment.
What Happens During the Test?
A healthcare provider will draw blood from a vein in your arm. The blood sample is sent to a lab for analysis. The test typically takes about 10–15 minutes, including the draw and processing.
What Are the Results Meaning?
Results are interpreted by your doctor based on your medical history, symptoms, and other test results. Elevated free cortisol may signal overproduction by the adrenal glands, while low levels could indicate problems with production or regulation.
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 testing is critical for diagnosing conditions like Cushing’s syndrome (excess cortisol) or Addison’s disease (insufficient cortisol). It also helps differentiate between primary adrenal disorders and those involving the pituitary gland. Elevated or low cortisol can affect metabolism, blood pressure, and stress responses, so early detection is important for treatment planning.
Short name
Free Cortisol
Frequently asked questions
How often is a free cortisol test repeated?
What causes false high or low cortisol results?
Can lifestyle changes 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 17, 2026. · Read our editorial policy