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Cortisol, Free, Serum

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

This test measures the amount of free cortisol, a naturally occurring hormone produced by your adrenal glands, in your blood. Free cortisol is the active form that circulates in your bloodstream and is important for regulating stress responses, metabolism, and other bodily functions.

Quick summary

["Free cortisol helps your body manage stress and keeps vital functions balanced."]

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

Key facts at a glance

LOINC
50752-5
Short code
Cortis 15M p Ins IV SerPl-mCnc
Synonyms
Cortis 15M p Ins IV SerPl-mCnc
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 This Test Is Done

Your healthcare provider may order a free cortisol test to check for conditions like Cushing’s syndrome (overactive adrenal glands), adrenal insufficiency (underactive adrenal glands), or to monitor treatment for these conditions. It can also help diagnose hormonal imbalances or evaluate symptoms like unexplained weight changes, fatigue, or high blood pressure.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for a few hours before the blood draw. If you’re taking certain medications (like steroids), your provider may instruct you to stop them temporarily or adjust your timing. Always follow your provider’s specific instructions.

During the Test

A healthcare professional will draw blood from a vein in your arm. You may feel a slight pinch or discomfort, but it usually lasts only a few seconds. The blood sample will be sent to a lab for analysis.

What the Results Mean

Results are interpreted based on your symptoms, medical history, and other tests. High cortisol levels may suggest conditions like Cushing’s syndrome, while very low levels could indicate adrenal problems. Your provider will discuss the results in the context of your overall health.

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 levels can be caused by conditions like Cushing’s syndrome (due to excess hormone production), prolonged stress, certain medications (including steroids), or tumors affecting the adrenal glands or pituitary. Symptoms may include weight gain, fatigue, muscle weakness, or high blood pressure.
What causes low cortisol levels?
Low cortisol levels often result from adrenal insufficiency (such as Addison’s disease), where the adrenal glands don’t produce enough cortisol. This can happen due to autoimmune disorders, infections, or long-term steroid use. Symptoms may include dizziness, low blood pressure, fatigue, or weight loss.
Can free cortisol levels change with diet or exercise?
Yes, cortisol levels can fluctuate based on stress, time of day, and certain medications. For example, cortisol is naturally higher in the morning and lower at night. If your test is part of a diagnostic evaluation, your provider may recommend timing the test at a specific time (e.g., morning) for more accurate results.
  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