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Cortisol, Free, Serum

Published: August 9, 2026Updated: August 17, 2026

This test measures the amount of free (unbound) cortisol in your blood, a hormone produced by your adrenal glands that helps regulate stress responses, metabolism, and immune function.

Quick summary

["Free cortisol helps doctors assess adrenal gland function and potential adrenal insufficiency or excess."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
103647-4
Short code
Cortis 2h p ACTH SerPl-mCnc
Synonyms
Cortis 2h p ACTH SerPl-mCnc
Category
hormone
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
60
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 diagnose conditions like Cushing’s syndrome (overactive adrenal glands), adrenal insufficiency (underactive adrenal glands), or to monitor treatment for these conditions. It can also help evaluate stress-related hormonal imbalances or evaluate pituitary gland function, which controls cortisol production.

What Does the Result Mean?

Results are interpreted based on your clinical symptoms and other test results. Elevated levels may indicate Cushing’s syndrome or other causes of high cortisol, while low levels could suggest adrenal or pituitary issues. Your doctor will discuss these findings with you.

Sample Collection and Preparation

A blood sample is drawn from a vein in your arm. The sample is collected in a special tube to separate serum (the liquid part) for testing. Free cortisol is measured after the serum is prepared, ensuring only the unbound hormone is detected.

Common Conditions Monitored

This test is often used to monitor conditions such as adrenal tumors, pituitary tumors, or chronic stress-related cortisol dysregulation. It may also be part of a broader evaluation for unexplained fatigue, weight changes, or hormonal symptoms.

Reference range

NCBI: ACTH 10-60 pg/mLN/A

Specimen: serum

Typically collected in the morning (8-10 AM). Inform your provider if taking steroid 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 free cortisol level mean?
A high free cortisol level may suggest conditions like Cushing’s syndrome, where the adrenal glands produce too much cortisol, or certain medications that increase cortisol. It can also be caused by prolonged stress or tumors affecting hormone production.
What does a low free cortisol level mean?
Low free cortisol levels may indicate adrenal insufficiency (Addison’s disease) or problems with the pituitary gland, which controls cortisol release. This can lead to symptoms like fatigue, weight loss, or low blood pressure.
How often should I get this test?
Your doctor will determine the frequency based on your symptoms, diagnosis, or treatment plan. Some patients may need this test periodically to monitor hormone levels, while others may only need it once for diagnosis.
  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 17, 2026. · Read our editorial policy