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Cortisol, Free, Serum

Published: August 9, 2026Updated: August 17, 2026

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

Quick summary

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

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
49969-9
Short code
Cortis 30M p 250 ug ACTH IM SerPl-SCDiff
Synonyms
Cortis 30M p 250 ug ACTH IM SerPl-SCDiff
Category
hormone
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
60
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 insufficiency or hypercortisolism (e.g., high blood sugar, muscle weakness, or mood changes). It could also be used to evaluate conditions like Cushing’s syndrome or Addison’s disease.

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 draw if cortisol levels are being measured at specific times (e.g., morning or evening). If you’re taking medications that affect cortisol, let your provider know.

How the Test Is Performed

A blood sample is taken from a vein in your arm by a healthcare professional. The sample is then sent to a lab for analysis using a sensitive immunoassay method to measure free cortisol levels.

What the Results Mean

Results are compared to reference ranges for your age, sex, and health status. Abnormally high or low levels may indicate underlying medical conditions that require further evaluation, such as hormonal disorders or stress-related issues.

Reference range

NCBI: ACTH 10-60 pg/mLN/A

Specimen: serum

Typically collected in the morning (8-10 AM). Inform your provider if taking steroid medications.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Cortisol

Frequently asked questions

What causes false high or low cortisol results?
False results can occur due to recent stress, certain medications (e.g., steroids), or improper sample handling. If your results are unclear, your provider may repeat the test or order additional tests to confirm findings.
How often should I get this test?
The frequency depends on your health status and symptoms. Your provider will determine if repeat testing is needed, especially if you have ongoing concerns about hormone balance or adrenal function.
Can diet or exercise affect cortisol levels?
Yes, diet (e.g., high sugar or caffeine intake), exercise, and sleep quality can influence cortisol levels. Avoiding extreme stress and maintaining a balanced lifestyle may help support normal hormone function.
  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 17, 2026. · Read our editorial policy