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Cortisol, Free (Serum)

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

["Free cortisol helps your body manage stress and maintain balance in key bodily functions."]

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

Key facts at a glance

LOINC
58670-1
Short code
Cortis 45M p 1 ug/kg CRH IV Sal-mCnc
Synonyms
Cortis 45M p 1 ug/kg CRH IV Sal-mCnc
Category
hormone
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
86701
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 doctor may order a free cortisol test to diagnose or monitor conditions like Cushing’s syndrome (excess cortisol), Addison’s disease (low cortisol), or adrenal insufficiency. It can also help assess stress-related hormone imbalances or evaluate symptoms like fatigue, weight changes, or mood swings.

What to Expect Before the Test

No special preparation is needed, but you may be asked to avoid certain medications (like steroids) that could affect results. If you’re taking them, tell your doctor. Bring a list of all medications, including over-the-counter items.

How the Test Works

A blood sample is taken from a vein in your arm. The sample is sent to a lab where cortisol is measured using a sensitive immunoassay method to detect even small amounts.

What the Results Mean

Results are compared to reference ranges for free cortisol in serum. Abnormally high or low levels may indicate hormonal disorders, but 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.

Clinical Significance: Free cortisol is a key hormone in the body’s stress response system. High levels may signal conditions like Cushing’s syndrome (from tumors or excess hormone production), while low levels can indicate adrenal insufficiency (Addison’s disease) or pituitary issues. Frequent monitoring may be needed if you have chronic stress, weight fluctuations, or unexplained fatigue.

Short name

Free Cortisol

Frequently asked questions

How often should I get this test?
The frequency depends on your health condition and doctor’s recommendations. For example, someone with suspected Cushing’s syndrome might need multiple tests over days or weeks to confirm results. Your doctor will guide you on timing and repeat testing if needed.
What causes false high or low results?
False high results can occur if you’re taking certain medications (like steroids), have recent stress, or had recent trauma. False low results may happen if you’re dehydrated, have recent illness, or if the sample was improperly handled. Always follow your doctor’s instructions for preparation.
Can I eat or drink before this test?
You can eat and drink normally unless instructed otherwise. Some tests may require fasting, but this one does not. Avoid caffeine or alcohol in the 24 hours before testing, as they can temporarily 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