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Cortisol, Free (Serum/Plasma)

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

This test measures the amount of free cortisol, a form of the hormone cortisol that is not bound to proteins in your blood. Free cortisol is important for regulating stress responses, metabolism, and other bodily functions.

Quick summary

["Free cortisol helps your body manage stress and maintain balance in your hormones and metabolism."]

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

Key facts at a glance

LOINC
9812-9
Short code
Cortis PM SerPl-mCnc
Synonyms
Cortis PM 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 Is This Test Done?

Your healthcare provider may order a free cortisol test to check for conditions like Cushing’s syndrome (a hormonal disorder caused by too much cortisol) or adrenal insufficiency (when your adrenal glands don’t produce enough cortisol). It can also help diagnose issues related to stress responses or hormone imbalances.

How Is the Sample Collected?

A blood sample is taken from a vein in your arm. You may feel a small pinch when the needle is inserted, but the procedure is quick. The blood is placed in a special tube to separate the serum or plasma from blood cells for testing.

What Should You Do Before the Test?

If your test is part of a stress response evaluation, you may need to fast for a few hours before the test or follow specific instructions to avoid interfering substances. Always follow your provider’s instructions carefully.

What Are Common Results?

Results are typically reported as a concentration of cortisol in the blood. Since reference ranges can vary by lab and individual factors, your results will be compared to your own baseline or clinical context rather than a single general range.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Cortisol

Frequently asked questions

What does a free cortisol test measure?
A free cortisol test measures the amount of cortisol that is not attached to proteins in your blood, which reflects your body’s active hormone levels. This helps determine if your cortisol production is too high or too low.
Why might my doctor order a free cortisol test?
Your doctor may order this test to diagnose conditions like Cushing’s syndrome, adrenal insufficiency, or to evaluate how your body responds to stress. It can also help monitor certain hormonal or metabolic disorders.
Can I eat or drink anything before this test?
Follow your healthcare provider’s instructions regarding food, drink, or activity before the test. Some tests may require fasting or avoiding certain medications to get 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