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Cortisol, Free (Serum or Plasma)

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

This test measures the amount of free cortisol, a form of the hormone cortisol that circulates freely in your blood. Free cortisol is important for managing stress, immune response, and metabolism.

Quick summary

["Free cortisol helps regulate how your body responds to stress and maintains balance in your hormones."]

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

Key facts at a glance

LOINC
54214-2
Short code
Cortis 5D p Dex SerPl-sCnc
Synonyms
Cortis 5D p Dex SerPl-sCnc
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 a free cortisol test to check for conditions like Cushing’s syndrome (overactive cortisol production), adrenal insufficiency (underactive adrenal glands), or to monitor treatment for hormone-related disorders. It can also help diagnose issues with your pituitary gland, which controls cortisol production.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to avoid certain medications or supplements that could affect results. If you’re taking corticosteroids (like prednisone), your doctor may instruct you to stop temporarily or adjust timing.

How the Test Is Performed

A blood sample is drawn from a vein in your arm, typically in a clinic or doctor’s office. The sample is sent to a lab for analysis using a sensitive immunoassay method to measure free cortisol levels.

What the Results Mean

Results are compared to reference ranges for your age and sex, but exact values can vary by lab. High free cortisol may indicate overproduction (e.g., from tumors or excess stress), while low levels could signal adrenal or pituitary issues. Your doctor will interpret results in the context of your symptoms and medical history.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Cortisol

Frequently asked questions

How is free cortisol different from total cortisol?
Free cortisol is the portion of cortisol that isn’t bound to proteins in your blood and thus directly available to your body’s tissues. Total cortisol includes both free and bound cortisol, so free cortisol testing provides a more accurate reflection of biologically active hormone levels.
Can stress affect my free cortisol test results?
Yes, stress can temporarily raise cortisol levels. If your test is scheduled during a stressful period (e.g., surgery, illness), your doctor may recommend retesting later or using a 24-hour urine cortisol test for more reliable results.
Is fasting required for this test?
No fasting is typically required, but if you’re taking medications that affect cortisol (like some antidepressants or steroids), your doctor may advise timing your test around when you take them for consistency.
  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