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Serum/plasma free cortisol concentration

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

This test measures the amount of cortisol (a stress hormone) that is not bound to proteins in your blood, helping assess adrenal function and potential hormone imbalances.

Quick summary

["Free cortisol levels can indicate adrenal gland health and response to stress."]

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

Key facts at a glance

LOINC
56571-3
Short code
GH p Exc SerPl-mCnc
Synonyms
GH p Exc SerPl-mCnc
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 if you have symptoms like unexplained weight changes, fatigue, mood swings, or signs of hormonal imbalances. It’s also used to diagnose conditions such as Cushing’s syndrome or adrenal insufficiency.

What to Expect Before the Test

No special preparation is needed, but you may be asked to avoid certain medications that could affect results. If you’re taking corticosteroids or other stress-related medications, let your provider know.

How the Test Works

A blood sample is drawn from a vein, typically in your arm. The sample is processed to separate free cortisol from protein-bound forms before analysis.

Possible Results and Next Steps

Results are compared to general reference ranges for free cortisol. Abnormal levels may prompt further testing, such as a 24-hour urine cortisol collection or additional hormone evaluations.

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 free cortisol level mean?
A high free cortisol level may suggest conditions like Cushing’s syndrome, where the body produces too much cortisol. Your provider will discuss further testing or treatment options based on the results.
What does a low free cortisol level mean?
A low free cortisol level may indicate adrenal insufficiency, where the adrenal glands don’t produce enough cortisol. This can be due to underlying health issues or medications. Your provider will work with you to determine the cause and appropriate care.
How often should I get this test?
The frequency depends on your symptoms, medical history, and treatment plan. Your healthcare provider will let you know if follow-up testing is needed.
  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