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Cortisol, Serum (Free Cortisol)

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

This test measures the amount of free cortisol, a form of the hormone cortisol, in your blood. Free cortisol is the active, unbound portion that circulates freely in your serum.

Quick summary

["This test helps assess adrenal function and hormone balance, often used in diagnosing 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
1398-7
Short code
Cortis 1.5h p Ins IV SerPl-mCnc
Synonyms
Cortis 1.5h p Ins IV 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 This Test Is Done

Your healthcare provider may order a free cortisol test to evaluate adrenal gland function, check for hormonal imbalances, or diagnose conditions such as Cushing’s syndrome (excess cortisol) or Addison’s disease (low cortisol). It can also be used to monitor treatment for these conditions or other endocrine disorders.

What to Expect Before the Test

No special preparation is usually needed. You may be asked to fast for 8–12 hours before the test if timing your cortisol levels around certain times of the day is important. Bring any medications you’re taking to your appointment.

What Happens During the Test

A healthcare professional will draw blood from a vein in your arm. The blood sample will be sent to a lab for analysis. Free cortisol is measured in the serum portion of your blood.

What the Results Mean

Results help determine whether your cortisol levels are too high or too low. Abnormal results may indicate conditions affecting your adrenal glands, pituitary gland, or other hormonal systems. Your doctor will interpret the results in the context of your symptoms and medical history.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Free Cortisol

Frequently asked questions

What are the normal reference ranges for this test?
Normal reference ranges can vary by lab and may depend on the time of day the sample was collected. Your doctor will provide specific guidance based on your test results and clinical needs. Free cortisol levels are often measured in nanograms per deciliter (ng/dL) or picomoles per liter (pmol/L).
How often should I get this test?
The frequency of this test depends on your medical condition and treatment plan. Your doctor will determine how often you need retesting, whether it’s part of routine monitoring or in response to specific symptoms or changes in your health.
Can I take anything before this test?
If your doctor specifies timing for cortisol levels (e.g., morning or evening), follow their instructions carefully. Avoid smoking, caffeine, or strenuous activity for a few hours before the test. Always inform your doctor about any medications you’re taking, as some may affect cortisol levels.
  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