Cortisol, Plasma, Free (Mass Concentration)
This test measures the amount of free (unbound) cortisol in your plasma. Cortisol is a hormone produced by your adrenal glands and plays a key role in managing stress, immune response, and metabolism.
["Free cortisol levels help diagnose conditions like Cushing’s syndrome or adrenal insufficiency."]
Key facts at a glance
- LOINC
- 1363-1
- Short code
- ACTH 30M p Ins IV Plas-mCnc
- Synonyms
- ACTH 30M p Ins IV Plas-mCnc
- Category
- hormone
- Sample
- plasma
- Container
- Lavender-top (EDTA) or Green-top (Heparin)
- 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 This Test Might Be Ordered
Your doctor may recommend this test if they suspect hormonal imbalances, such as an overactive or underactive adrenal gland, or to evaluate conditions like Cushing’s disease or Addison’s disease. It may also be used to monitor treatment responses for these conditions.
What to Expect Before the Test
No special preparation is needed for this test. You may have a blood sample drawn from a vein in your arm, similar to other routine blood tests. If you’re taking medications that affect cortisol levels, like steroids, let your healthcare provider know.
What the Results Mean
Results are interpreted by your healthcare provider based on your overall health, symptoms, and other test results. Elevated levels might indicate conditions like Cushing’s syndrome, while low levels could suggest adrenal insufficiency or other hormonal disorders.
Common Conditions This Test Helps Diagnose
This test is often used to diagnose or monitor conditions linked to abnormal cortisol production, such as Cushing’s disease (caused by a pituitary tumor), adrenal insufficiency (Addison’s disease), or ectopic ACTH syndrome (cortisol-producing tumors outside the pituitary).
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 are critical for diagnosing conditions where cortisol regulation is disrupted. Accurate measurement helps differentiate between primary adrenal disorders and those caused by pituitary or other hormonal imbalances. It’s also useful for assessing treatment efficacy in patients on steroid therapy or managing stress-related cortisol fluctuations.
Short name
Free Plasma Cortisol
Frequently asked questions
What does a free cortisol test measure?
Why might my doctor order a free cortisol test?
Can food or medications affect cortisol test results?
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