Cortisol, Free, Serum or Plasma
This test measures the amount of free (unbound) cortisol, a hormone produced by your adrenal glands, in your blood. Free cortisol reflects your body’s current cortisol levels without interference from proteins that normally carry cortisol in the blood.
["Free cortisol helps assess adrenal gland function and hormone imbalances."]
Key facts at a glance
- LOINC
- 57825-2
- Short code
- Cortis F PM SerPl-mCnc
- Synonyms
- Cortis F PM 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 a free cortisol test to check for conditions like Cushing’s syndrome (overproduction of cortisol) or adrenal insufficiency (underproduction). It can also help diagnose other hormonal disorders or evaluate symptoms like fatigue, weight changes, or unusual mood swings.
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 blood draw if timing your cortisol levels around a specific time of day (morning or evening) is important. Bring any medications you’re taking to your appointment.
How the Test Is Performed
A healthcare professional will draw blood from a vein in your arm using a small needle. You may feel a brief pinch, but the procedure is quick. The blood sample is sent to a lab for analysis using an immunoassay method to measure free cortisol levels.
What the Results Mean
Results are compared to general reference ranges, but your actual values may vary based on your age, health, and other factors. High cortisol levels may suggest Cushing’s syndrome or stress-related overproduction, while low levels could indicate adrenal problems. Your doctor will interpret results in the context of your symptoms and medical history.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Cortisol is a stress hormone that helps regulate metabolism, immune response, and blood pressure. Chronic high cortisol can lead to weight gain, high blood pressure, or weakened immune function, while low cortisol may cause fatigue, dizziness, or difficulty handling stress. Free cortisol testing helps identify whether hormonal imbalances are affecting your health.
Short name
Free Cortisol
Frequently asked questions
What causes abnormal cortisol levels?
How often should I get this test?
Can lifestyle changes affect cortisol test results?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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