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Free Cortisol (Serum/Plasma)

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

This test measures the amount of cortisol that is not bound to proteins in your blood, providing insight into your body’s natural cortisol levels.

Quick summary

["Free cortisol helps assess adrenal function and potential hormone imbalances."]

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

Key facts at a glance

LOINC
76475-3
Short code
Cortisone free SerPl-sCnc
Synonyms
Cortisone free SerPl-sCnc
Category
chemistry
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 healthcare provider may order this test to evaluate conditions affecting your adrenal glands, such as Cushing’s syndrome (too much cortisol) or Addison’s disease (too little cortisol). It can also help diagnose or monitor adrenal insufficiency, hormonal disorders, or reactions to medications that affect cortisol levels.

What to Expect Before the Test

No special preparation is typically needed. You may be asked to fast for 8–12 hours before the test if your provider recommends it, but this depends on the lab’s protocol. Bring any medications you’re taking to your appointment.

How the Test Is Performed

A blood sample is drawn from a vein, usually in your arm. The sample is sent to a lab for analysis using a sensitive immunoassay method to measure free cortisol levels.

What the Results Mean

Results are compared to reference ranges for your age, sex, and health status. Abnormal levels may indicate hormonal imbalances or conditions affecting cortisol production.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Cortisol

Frequently asked questions

What causes free cortisol levels to be tested?
Free cortisol testing is often done when symptoms like weight gain, fatigue, high blood pressure, or muscle weakness suggest hormonal imbalances. It may also be used to monitor treatment for conditions like Cushing’s syndrome or adrenal disorders.
How long does it take to get the results?
Results are typically available within 1–3 business days, depending on the lab. Your healthcare provider will discuss them with you during your follow-up visit.
Can I take anything before the test?
Follow your provider’s instructions—some tests require fasting, while others do not. Always check with your lab or provider before making changes to your routine.
  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