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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 that circulates freely in your blood. Cortisol is involved in regulating metabolism, immune response, and stress reactions.

Quick summary

["Free cortisol helps assess adrenal gland function and hormone balance."]

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

Key facts at a glance

LOINC
54213-4
Short code
Cortis 4D p Dex SerPl-sCnc
Synonyms
Cortis 4D p 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 healthcare provider may order this test to evaluate conditions affecting your adrenal glands, such as Cushing’s syndrome (overactive cortisol production) or Addison’s disease (underactive cortisol production). It can also help diagnose adrenal insufficiency or monitor treatment for hormone-related disorders.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the test if cortisol levels are being measured at specific times (e.g., morning or evening). Bring any medications you’re taking to your appointment.

How the Test Is Performed

A blood sample is drawn from a vein in your arm by a healthcare professional. The sample is sent to a lab for analysis using a sensitive immunoassay method to detect free cortisol levels.

What the Results Mean

Results are compared to standard reference ranges for free cortisol in serum. Abnormally high or low levels may indicate hormonal imbalances or underlying health conditions requiring further evaluation.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Cortisol

Frequently asked questions

What causes false high or low cortisol results?
False results can occur due to recent stress, certain medications (e.g., steroids), or improper sample handling. If your results are unclear, your provider may repeat the test or order additional tests for confirmation.
How often should I get this test?
The frequency depends on your health condition and treatment plan. Your healthcare provider will determine if regular monitoring is needed, such as for chronic hormone disorders or before starting certain medications.
Can lifestyle changes affect cortisol levels?
Yes, stress, sleep patterns, diet, and exercise can influence cortisol levels. Maintaining a consistent routine and managing stress may help support healthy hormone balance, but this test alone cannot replace professional medical advice.
  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