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Cortisol, Free, Serum

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

This test measures the amount of free (unbound) cortisol in your blood, a hormone produced by your adrenal glands that helps regulate metabolism, immune response, and stress reactions.

Quick summary

["Free cortisol helps assess adrenal function and potential hormone imbalances."]

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

Key facts at a glance

LOINC
58643-8
Short code
Cortis 12 AM Sal-sCnc
Synonyms
Cortis 12 AM Sal-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 Might Be Ordered

Your healthcare provider may recommend this test if you have symptoms like unexplained weight changes, fatigue, high blood pressure, or signs of adrenal gland issues. It could also be part of diagnosing conditions such as Cushing’s syndrome, adrenal insufficiency, or other hormonal disorders.

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 your provider specifies it. Bring any medications you’re currently taking, as they may affect results.

During the Test

A healthcare professional will draw blood from a vein in your arm. You may feel a slight pinch, but the process is quick and typically painless. The blood sample will be sent to a lab for analysis.

What the Results Mean

Results help determine if your cortisol levels are too high or too low, which can indicate underlying health issues. Your provider will interpret the results in relation to your symptoms and medical history.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Cortisol plays a critical role in managing stress, immune function, and metabolism. Abnormal levels may signal conditions like adrenal gland disorders, hormonal imbalances, or other systemic health concerns that require further medical evaluation.

Short name

Free Cortisol

Frequently asked questions

What triggers cortisol levels to change?
Cortisol levels naturally fluctuate throughout the day, peaking in the early morning and dropping at night. Stress, physical activity, illness, or certain medications can also temporarily alter cortisol levels. If you’re taking medications like steroids, let your provider know as it may affect test results.
How often should I get this test?
The frequency depends on your symptoms and medical needs. Your provider will determine how often to repeat the test based on your diagnosis, treatment plan, or ongoing health concerns.
Can diet or lifestyle affect cortisol test results?
Yes, diet, stress levels, and physical activity can influence cortisol levels. Avoiding caffeine, alcohol, or intense exercise for 24 hours before the test may help provide more accurate results. Follow your provider’s specific instructions for optimal testing conditions.
  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