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Serum or Plasma Immunoassay for Free Cortisol

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

This test measures the amount of cortisol (a stress hormone) that is not bound to proteins in your blood, helping assess adrenal function and potential stress-related conditions.

Quick summary

["Free cortisol levels can indicate how well your body manages stress responses and rule out adrenal disorders."]

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

Key facts at a glance

LOINC
110779-6
Short code
YFV IgG Msmt Ser
Synonyms
YFV IgG Msmt Ser
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
82784
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 a free cortisol test if you have symptoms like unexplained fatigue, weight changes, or signs of adrenal insufficiency (such as low blood pressure or salt cravings). It may also be used in diagnosing conditions like Cushing’s syndrome or adrenal tumors.

What to Expect Before the Test

No special preparation is needed, but you may be asked to avoid certain medications (like steroids) that can affect cortisol levels. If you’re taking them, your doctor will likely instruct you to stop temporarily or adjust your timing.

During the Test

A blood sample is drawn from a vein in your arm. You may feel a slight pinch, but it usually doesn’t cause significant discomfort. The sample is then sent to a lab for analysis.

What the Results Mean

Results help determine if your adrenal glands are producing cortisol at normal or abnormal levels. High or low free cortisol can signal conditions like hypercortisolism (e.g., Cushing’s syndrome) or hypocortisolism (e.g., Addison’s disease). Your doctor will interpret the results in the context of your symptoms and other tests.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Cortisol

Frequently asked questions

What could cause abnormal results?
Abnormally high free cortisol can be caused by conditions like Cushing’s syndrome (due to excess cortisol from tumors or medications), chronic stress, or certain medications. Low free cortisol may indicate adrenal insufficiency, pituitary disorders, or severe illness. Always discuss results with your healthcare provider.
How often should I get this test?
The frequency depends on your symptoms and diagnosis. Your doctor may recommend retesting if you have recurring stress, weight changes, or other concerning signs. Follow-up tests could include additional cortisol measurements or imaging studies.
Does this test interact with other medications?
Yes, certain medications—such as steroids (e.g., prednisone), birth control pills, or some antidepressants—can affect cortisol levels. If you’re taking any of these, inform your doctor before the test to adjust timing or dosage if needed.
  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