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Cortisol, Free (Serum/Plasma)

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of free (unbound) cortisol, a key hormone produced by your adrenal glands that helps regulate stress, metabolism, and immune response.

Quick summary

["Free cortisol helps diagnose conditions like Cushing’s syndrome or adrenal insufficiency."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
1439-9
Short code
Cortis 9.5h p 8 mg Dex SerPl-mCnc
Synonyms
Cortis 9.5h p 8 mg Dex 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 This Test Is Done

Your doctor may order this test to check for hormonal imbalances, evaluate symptoms like unexplained weight changes, fatigue, or high blood pressure, or confirm diagnoses such as Cushing’s syndrome (too much cortisol) or adrenal gland disorders.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the blood draw if timing your cortisol levels around a specific time of day is important.

How the Test Works

A blood sample is taken from a vein in your arm. The sample is then analyzed to measure the free cortisol concentration in your serum or plasma.

Possible Results and Interpretation

Results are compared to reference ranges for free cortisol, which can vary slightly by lab. Abnormal levels may indicate conditions requiring further medical evaluation.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

High cortisol levels may suggest Cushing’s syndrome, chronic stress, or other adrenal or pituitary disorders. Low cortisol levels could indicate adrenal insufficiency, Addison’s disease, or problems with the hypothalamus or pituitary gland. Your doctor will consider your symptoms and other test results to guide diagnosis and treatment.

Short name

Free Cortisol

Frequently asked questions

What does a high free cortisol level mean?
A high free cortisol level may signal excessive production of cortisol, which can be caused by conditions like Cushing’s syndrome (due to tumors or prolonged steroid use), prolonged stress, or certain medications. Further testing, such as a 24-hour urine cortisol test or dexamethasone suppression test, may be needed to determine the cause.
What does a low free cortisol level mean?
Low free cortisol levels often point to adrenal insufficiency (e.g., Addison’s disease), where the adrenal glands don’t produce enough cortisol. This can be congenital or develop from autoimmune diseases, infections, or long-term steroid withdrawal. Your doctor may recommend additional tests or treatment to manage symptoms.
Can diet or supplements affect cortisol levels?
Yes, certain foods, caffeine, alcohol, and some supplements (like adaptogens) can temporarily influence cortisol levels. Avoiding stimulants and stress triggers for a few days before testing may help provide more accurate results.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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