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Cortisol, Free (Serum or Plasma)

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. Free cortisol is important for regulating metabolism, immune response, and stress reactions.

Quick summary

["Your doctor may check free cortisol to diagnose or monitor conditions like Cushing’s syndrome or adrenal gland issues."]

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

Key facts at a glance

LOINC
55348-7
Short code
Cortis 20M p chal SerPl-sCnc
Synonyms
Cortis 20M 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 This Test Is Done

Your healthcare provider may order a free cortisol test if you have symptoms of hormonal imbalances, such as unexplained weight changes, high blood pressure, or unusual fatigue. It could also be used to evaluate conditions like adrenal insufficiency, Cushing’s syndrome, or to check for cortisol-related disorders before surgery or during treatment for certain cancers.

What to Expect During the Test

A blood sample is taken from a vein in your arm. You may feel a small pinch when the needle is inserted, but the procedure usually takes only a few minutes. You can resume normal activities afterward.

Sample Collection and Preparation

The test uses either serum (blood without clotting factors) or plasma (blood with clotting factors removed). The sample is sent to a lab for measurement using a sensitive immunoassay method to detect cortisol levels accurately.

What the Results Mean

Results help determine if your cortisol levels are too high or too low, which can indicate underlying health conditions. Your doctor will compare your results to your baseline and other test findings to make a diagnosis.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Free Cortisol

Frequently asked questions

What does cortisol do in the body?
Cortisol is a steroid hormone produced by your adrenal glands. It plays a key role in managing stress, controlling blood sugar levels, and supporting immune responses. Free cortisol is particularly important because it reflects the active, biologically available form of the hormone in your bloodstream.
How often should I get this test?
The frequency of this test depends on your medical condition and treatment plan. Your doctor will schedule follow-up tests based on their assessment of your health and response to treatment. Regular monitoring may be needed if you have chronic conditions like Cushing’s syndrome or adrenal insufficiency.
Can diet or lifestyle affect cortisol levels?
Yes, lifestyle factors such as stress, sleep quality, and diet can influence cortisol levels. Chronic stress, poor sleep, or high-sugar diets may temporarily elevate cortisol. If you suspect lifestyle changes are affecting your results, discuss this with your healthcare provider to explore adjustments that may help.
  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