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Cortisol, Serum (Free)

Published: August 9, 2026Updated: August 17, 2026

This test measures the amount of free cortisol, a form of the hormone cortisol, in your blood. Free cortisol is the active, non-protein-bound form that circulates freely in your bloodstream and is available to bind to receptors in your body.

Quick summary

["Free cortisol helps regulate stress responses and metabolism; abnormal levels may indicate conditions like Cushing’s syndrome or adrenal insufficiency."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
34476-2
Short code
Cortis 1h p 250 ug ACTH SerPl-mCnc
Synonyms
Cortis 1h p 250 ug ACTH SerPl-mCnc
Category
hormone
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
60
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 Is This Test Done?

Your doctor may order this test to diagnose or monitor conditions affecting your adrenal glands, such as Cushing’s syndrome (too much cortisol) or adrenal insufficiency (too little cortisol). It can also help evaluate symptoms like unexplained weight changes, fatigue, or high blood pressure linked to hormonal imbalances.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8 hours before the test if cortisol levels are being measured at specific times of the day. Bring any medications you’re currently taking to your appointment.

How the Test Works

A blood sample is drawn from a vein in your arm. The sample is then analyzed using a sensitive immunoassay method to measure free cortisol levels in your serum.

What the Results Mean

Results are compared to general reference ranges for cortisol, though individual ranges may vary by lab. High levels may suggest overproduction of cortisol, while low levels could indicate adrenal gland dysfunction or other hormonal issues.

Reference range

NCBI: ACTH 10-60 pg/mLN/A

Specimen: serum

Typically collected in the morning (8-10 AM). Inform your provider if taking steroid medications.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Cortisol

Frequently asked questions

What causes abnormal cortisol levels?
Abnormal cortisol levels can result from conditions like Cushing’s syndrome (due to excess cortisol production), adrenal insufficiency (due to insufficient cortisol production), or certain medications (e.g., steroids). Stress, thyroid disorders, or tumors in the pituitary gland may also influence results.
How long does it take to get my results?
Results are typically available within 1 to 3 business days, depending on your lab’s processing time. Your healthcare provider will discuss the findings with you during your follow-up visit.
Can I take anything before my cortisol test?
Avoid smoking, caffeine, or alcohol for 24 hours before testing. If your doctor prescribed medications, ask whether to pause them temporarily or take them as usual. Follow any fasting instructions provided if applicable.
  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 17, 2026. · Read our editorial policy