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Cortisol, Free (Serum/Plasma)

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

This test measures the amount of free cortisol, a hormone produced by your adrenal glands, in your blood. Free cortisol is the active form that travels freely in your bloodstream and is important for managing stress responses and other bodily functions.

Quick summary

["Free cortisol helps regulate stress, metabolism, and immune response."]

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

Key facts at a glance

LOINC
16672-8
Short code
Cortis 40M p chal SerPl-mCnc
Synonyms
Cortis 40M p chal 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 Is This Test Done?

Your healthcare provider may order this test to check for conditions like Cushing’s syndrome (overproduction of cortisol), adrenal insufficiency (underproduction), or to monitor treatment for hormone-related disorders. It can also help diagnose issues with cortisol’s role in stress responses or other hormonal imbalances.

What to Expect Before the Test

No special preparation is usually 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). Blood is drawn from a vein in your arm.

How the Test Works

A small amount of blood is taken to measure free cortisol levels. The test detects cortisol that is not bound to proteins, ensuring accurate reflection of biologically active hormone levels.

What the Results Mean

Results are interpreted by your healthcare provider based on your symptoms, medical history, and timing of the test. Abnormal results may indicate hormonal imbalances that require 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 abnormal cortisol levels?
Abnormal cortisol levels can result from conditions like Cushing’s syndrome (too much cortisol), adrenal insufficiency (too little cortisol), or stress-related fluctuations. Other factors, such as medications (e.g., steroids) or certain medical treatments, may also affect results.
How often should I get this test?
Your healthcare provider will determine how often you need this test based on your symptoms, diagnosis, or treatment plan. Some people may need it once, while others may require regular monitoring.
Can diet or medications affect cortisol test results?
Yes, certain foods, medications (including steroids), caffeine, or stress can influence cortisol levels. Follow your provider’s instructions for fasting or timing to ensure accurate results.
  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