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Cortisol, Serum (Free)

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

This test measures the amount of free cortisol, a form of the hormone cortisol found naturally in your blood. Free cortisol is the active form that can cross cell membranes and regulate various bodily functions.

Quick summary

["Free cortisol helps balance stress, metabolism, and immune responses, and abnormal levels may signal health concerns like adrenal disorders or Cushing’s syndrome."]

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

Key facts at a glance

LOINC
100662-6
Short code
CORTO SerPl
Synonyms
CORTO SerPl
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 Is This Test Done?

Your doctor may order this test to evaluate adrenal gland function, check for conditions like Cushing’s syndrome (too much cortisol), Addison’s disease (too little cortisol), 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 if you’re taking medications that affect cortisol levels (like steroids), your doctor may ask you to stop them temporarily or adjust timing. Avoiding caffeine or alcohol for a few hours before the test can help ensure accurate results.

How the Test Works

A blood sample is drawn from a vein, usually in your arm. The sample is then processed to measure free cortisol levels, which are distinct from total cortisol (which includes bound forms). Free cortisol is typically analyzed using a sensitive immunoassay method.

What the Results Mean

Results are compared to reference ranges for your age and sex, but these can vary by lab. High cortisol levels may indicate overactivity of the adrenal glands or pituitary gland, while low levels could signal adrenal insufficiency or other hormonal imbalances. 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.

Clinical Significance

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), Addison’s disease (due to adrenal insufficiency), or medications (such as steroids). Stress, certain tumors, or genetic disorders can also affect cortisol metabolism. Chronic stress or sleep disorders may also influence cortisol timing.
How do I prepare for follow-up tests if my results are abnormal?
If your free cortisol test results are abnormal, your doctor may recommend additional tests, such as a 24-hour urine cortisol test, a dexamethasone suppression test, or monitoring cortisol levels at different times of day. Follow your doctor’s instructions carefully for any follow-up steps, including dietary or medication adjustments.
Can lifestyle changes affect cortisol levels?
Yes, lifestyle factors like sleep quality, stress levels, caffeine intake, and physical activity can influence cortisol. Maintaining a consistent sleep schedule, managing stress through relaxation techniques, and avoiding excessive caffeine can help support accurate test results and overall adrenal health.
  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