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Free Cortisol (Serum)

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

This test measures the amount of cortisol that is *not* bound to proteins in your blood, helping assess your body’s cortisol levels independently of protein carriers.

Quick summary

["Free cortisol helps evaluate adrenal function and hormone balance."]

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

Key facts at a glance

LOINC
71805-6
Short code
Cortis F/Cortisone Free Ur-sRto
Synonyms
Cortis F/Cortisone Free Ur-sRto
Category
hormone
Sample
urine
Container
Sterile urine container
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
10 mL
Stability
Room temperature: 2h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why This Test Matters

Cortisol is a hormone produced by your adrenal glands that helps regulate stress responses, metabolism, and immune function. Free cortisol specifically reflects the biologically active portion of cortisol in your blood, which can be important for diagnosing conditions like Cushing’s syndrome or adrenal insufficiency.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the draw if cortisol timing is critical. Bring any medications you’re taking, as they may affect results.

How the Test Works

A blood sample is taken from a vein in your arm. The lab separates serum (the liquid part after clotting) and measures the free cortisol concentration using a sensitive immunoassay method.

Possible Results & Next Steps

Results are compared to reference ranges for your age and health status. Abnormal results may prompt further testing (e.g., 24-hour urine cortisol or ACTH stimulation tests) to identify causes like hormonal imbalances or tumors.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Free Cortisol

Frequently asked questions

What might cause abnormal free cortisol levels?
High free cortisol can signal conditions like Cushing’s syndrome (excess cortisol from tumors or prolonged steroid use), while low levels may indicate adrenal gland dysfunction (e.g., Addison’s disease) or pituitary issues.
How often should I get this test?
This test is typically ordered as part of a diagnostic workup for suspected hormonal disorders. Your doctor will determine frequency based on your symptoms and medical history.
Does diet or stress affect this test?
Cortisol fluctuates naturally with stress or meals, so results may vary. If timing is critical (e.g., for adrenal function), your doctor may specify a specific window (e.g., morning/evening samples).
  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