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Cortisol, Free (Serum/Plasma)

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

This test measures the amount of cortisol, a hormone produced by your adrenal glands, in your blood. Free cortisol refers to the unbound, active form of the hormone.

Quick summary

["Free cortisol helps regulate stress responses and other bodily functions."]

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

Key facts at a glance

LOINC
47845-3
Short code
Cortis p 1 mg Dex SerPl-sCnc
Synonyms
Cortis p 1 mg Dex SerPl-sCnc
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 a free cortisol test to check for conditions like Cushing’s syndrome (overactive adrenal glands), adrenal insufficiency (underactive adrenal glands), or to evaluate stress-related hormone imbalances. It can also help diagnose pituitary disorders or monitor treatment for hormone-related conditions.

How Is the Sample Collected?

A blood sample is drawn from a vein, usually in your arm. You may feel a slight pinch when the needle is inserted, but the procedure is quick. The sample is sent to a lab for testing.

What Does the Test Involve?

The test measures cortisol in its free (unbound) form, which is the biologically active portion. This avoids interference from proteins that normally bind cortisol in the blood.

What Are Common Uses?

Free cortisol testing is often used in combination with other tests, such as a 24-hour urine cortisol test, to confirm or rule out hormonal imbalances. It helps assess how your body responds to stress and certain medications.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Cortisol

Frequently asked questions

What Does a High or Low Free Cortisol Level Mean?
A high free cortisol level may signal conditions like Cushing’s syndrome, where the body produces too much cortisol. A low level could indicate adrenal insufficiency, where the body struggles to produce enough cortisol, often due to stress, medications, or underlying health issues.
How Often Should I Get This Test?
The frequency depends on your symptoms, medical history, and treatment plan. Your doctor will determine how often to repeat the test based on your specific needs, such as monitoring chronic conditions or evaluating responses to treatments.
Can I Take Anything Before the Test?
Follow your doctor’s instructions carefully. Some tests may require fasting or avoiding certain medications, but free cortisol tests often do not have strict dietary restrictions unless specified. Always confirm with your healthcare provider.
  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