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Cortisol, Free (Serum or Plasma)

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

This test measures the amount of free cortisol, a hormone produced by your adrenal glands, in your blood. Free cortisol is not bound to proteins and reflects your body’s current cortisol levels.

Quick summary

["Free cortisol helps regulate stress, immune response, and metabolism."]

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

Key facts at a glance

LOINC
1402-7
Short code
Cortis 1h p 250 ug ACTH rIV SerPl-mCnc
Synonyms
Cortis 1h p 250 ug ACTH rIV 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 This Test Might Be Ordered

Your healthcare provider may recommend this test if you have symptoms of adrenal gland issues, such as unexplained weight changes, fatigue, or mood swings. It could also be used to diagnose conditions like Cushing’s syndrome (too much cortisol) or Addison’s disease (too little cortisol).

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the test if your provider specifies it. Wear comfortable clothing and bring any medications you’re currently taking, as some may affect results.

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 protein-bound cortisol.

What the Results Mean

Results help determine whether your cortisol levels are too high or too low, guiding treatment decisions. Your provider will interpret the results in relation to your symptoms and medical history.

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.

Free cortisol testing is critical for diagnosing hormonal imbalances affecting stress response, metabolism, and immune function. Elevated or low levels may indicate conditions requiring medical attention, such as endocrine disorders or chronic stress-related syndromes.

Short name

Free Cortisol

Frequently asked questions

What causes false high or low results?
False results can occur if you take certain medications (like steroids), have recent stress, or if the sample was improperly handled. Your provider will review your medical history and test timing to ensure accuracy.
How often should I get this test?
The frequency depends on your symptoms and medical needs. Your provider will determine how often to repeat the test based on your diagnosis and treatment plan.
Can I eat or drink before this test?
If fasting is required, avoid food and liquids (except water) for 8–12 hours before the test. If not fasting, eat a normal meal as usual, but ask your provider for specifics.
  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