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Free cortisol (serum/plasma)

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

This test measures the amount of cortisol that is not bound to proteins in your blood, providing insight into your body’s natural cortisol production and regulation.

Quick summary

["Free cortisol helps assess adrenal function and potential hormone imbalances."]

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

Key facts at a glance

LOINC
53777-9
Short code
Cortisone free Ur-mCnc
Synonyms
Cortisone free Ur-mCnc
Category
chemistry
Sample
urine
Container
Sterile urine container
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
10 mL
Stability
Room temperature: 2h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why This Test Is Done

Your doctor may order a free cortisol test to diagnose conditions like Cushing’s syndrome (excess cortisol) or Addison’s disease (low cortisol). It can also help evaluate adrenal gland function, especially if symptoms such as fatigue, weight changes, or mood swings are present.

What to Expect Before the Test

No special preparation is needed for this blood test. You may be asked to fast for 8–12 hours before the draw, but this is not always required. Bring any medications you’re taking, as some may affect results.

How the Test Works

A blood sample is taken from a vein, usually in your arm. The sample is processed to separate free cortisol from protein-bound cortisol, which is then measured using a sensitive laboratory method.

Possible Results and Interpretation

Results are compared to reference ranges specific to your age, sex, and health status. Abnormally high or low levels may signal underlying conditions that need further evaluation.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Free cortisol is a key marker for diagnosing adrenal disorders. Elevated levels can indicate Cushing’s syndrome (due to excess cortisol from the adrenal glands or pituitary), while low levels may suggest Addison’s disease or other adrenal insufficiency. It also helps monitor treatment responses for hormone-related conditions.

Short name

Free Cortisol Level

Frequently asked questions

What causes abnormal free cortisol levels?
Abnormal free cortisol levels can result from conditions like Cushing’s syndrome (from tumors or prolonged steroid use), Addison’s disease (autoimmune adrenal failure), or rare genetic disorders. Stress, certain medications (e.g., steroids), or thyroid issues may also influence results.
How long does it take to get results?
Results are typically available within 1–3 business days, depending on your lab’s processing time. Follow-up with your doctor to discuss findings and next steps.
Can I take anything before the test?
Avoid smoking, caffeine, or strenuous activity 24 hours before testing. If your doctor prescribed specific preparations (e.g., fasting), follow those instructions exactly.
  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