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Cortisol, Free (Serum)

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

This test measures the amount of free cortisol, a form of the hormone cortisol that circulates freely in your blood, independent of protein binding.

Quick summary

["Free cortisol helps regulate stress responses and metabolism; abnormal levels may signal hormonal imbalances or conditions like Cushing’s syndrome or adrenal insufficiency."]

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

Key facts at a glance

LOINC
51424-0
Short code
Cortis pre/p chal SerPl-sCnc
Synonyms
Cortis pre/p chal 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 diagnose or monitor conditions affecting your adrenal glands, such as Cushing’s disease (overproduction) or adrenal insufficiency (underproduction). It can also help evaluate stress-related hormone dysfunction or rule out certain endocrine disorders.

What to Expect Before the Test

No special preparation is needed, but you may be asked to avoid certain medications (like steroids) that could affect cortisol levels. If you’re taking them, your doctor will note this on your test results. Bring a list of all current medications to your appointment.

During the Test

A blood sample will be drawn from a vein in your arm by a healthcare professional. You may feel a slight pinch, but it usually takes only a few minutes. The sample is then sent to a lab for analysis using an immunoassay method to measure free cortisol concentration.

What the Results Mean

Results are compared to reference ranges specific to your age, sex, and health status. Elevated levels may indicate conditions like Cushing’s syndrome, while low levels could suggest adrenal gland problems or other hormonal imbalances. Your doctor will interpret results in the context of your overall health and symptoms.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Free Cortisol

Frequently asked questions

What causes elevated cortisol levels?
Elevated free cortisol can result from conditions like Cushing’s syndrome (due to excess cortisol production from the adrenal glands or pituitary gland), prolonged stress, certain medications (e.g., steroids), or rare genetic disorders. Chronic stress or sleep disorders may also play a role.
What causes low cortisol levels?
Low free cortisol levels often point to adrenal insufficiency (Addison’s disease), where the adrenal glands fail to produce enough cortisol. This can occur due to autoimmune disorders, infections, trauma, or long-term steroid use. Other rare causes include pituitary gland issues or genetic disorders.
How often should this test be repeated?
Your doctor will determine the frequency of retesting based on your symptoms, medical history, and test results. If initial results are abnormal, follow-up tests may be scheduled to monitor progression or response to treatment, such as medication adjustments or further diagnostic procedures.
  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