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Cortisol, Free (Serum/Plasma)

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

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

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
101980-1
Short code
Gluc+som+cort p insu pnl SerPl
Synonyms
Gluc+som+cort p insu pnl SerPl
Category
glucose
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
true
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 Is This Test Done?

Your healthcare provider may order this test to evaluate conditions like Cushing’s syndrome (overactive adrenal glands), adrenal insufficiency (underactive adrenal glands), or to monitor treatment for hormone-related disorders. It can also help diagnose issues with cortisol metabolism or stress responses.

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 cortisol levels are being tracked over time. Stress or certain medications can affect results, so inform your provider of any recent changes.

How the Test Works

A blood sample is taken from a vein in your arm. The sample is then analyzed to measure free cortisol levels using a sensitive immunoassay method, which detects the hormone without interference from other substances in the blood.

What the Results Mean

Results are interpreted in the context of your symptoms, medical history, and other tests. Abnormal levels may indicate hormonal imbalances or conditions affecting adrenal function, but a single test alone rarely provides a definitive diagnosis.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Free Cortisol

Frequently asked questions

What causes high cortisol levels?
High cortisol can result from conditions like Cushing’s syndrome (due to excess hormone production), prolonged stress, or certain medications. Chronic stress, obesity, or tumors affecting the adrenal glands may also play a role.
What causes low cortisol levels?
Low cortisol may stem from adrenal insufficiency (e.g., Addison’s disease), pituitary disorders, or sudden withdrawal from corticosteroids. Rarely, genetic or autoimmune factors can contribute.
How often should this test be repeated?
Results may need follow-up testing if symptoms persist or if further evaluation is required. Your provider will determine the best timing based on your clinical needs, such as repeating tests over 24-hour periods or during stress triggers.
  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