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Cortisol, Serum (Free Cortisol)

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

This test measures the amount of free cortisol, a form of the hormone cortisol, in your blood. Cortisol helps regulate metabolism, immune response, and stress reactions.

Quick summary

["Free cortisol levels can help diagnose conditions related to adrenal gland function or stress responses."]

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

Key facts at a glance

LOINC
1421-7
Short code
Cortis 32h p 40 ug ACTH IM SerPl-mCnc
Synonyms
Cortis 32h p 40 ug ACTH IM SerPl-mCnc
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 Is This Test Done?

Your doctor may order this test to check for adrenal gland disorders, such as Cushing’s syndrome (too much cortisol) or Addison’s disease (too little cortisol). It can also help evaluate stress responses, hormone imbalances, or symptoms like fatigue, weight changes, or high blood pressure.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the test if instructed by your healthcare provider. Bring any medications you’re taking to your appointment.

What Happens During the Test?

A blood sample will be drawn from a vein in your arm. You may feel a slight pinch, but it usually takes only a few minutes. The sample is then sent to a lab for analysis.

What Do Results Mean?

Results are interpreted by your doctor based on your symptoms, medical history, and other test results. Abnormally high or low levels may indicate conditions requiring further evaluation.

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.

Clinical Significance: Cortisol plays a key role in managing stress, immune function, and metabolism. Abnormal levels can signal adrenal disorders, hormonal imbalances, or chronic stress. Your doctor will use these results alongside other tests to guide diagnosis and treatment.

Short name

Free Cortisol

Frequently asked questions

What causes cortisol levels to be tested?
Cortisol levels may be checked if you have symptoms like unexplained weight changes, fatigue, high blood pressure, or signs of hormonal imbalances. Doctors also use it to diagnose conditions like Cushing’s syndrome or Addison’s disease.
How is cortisol measured in the blood?
Cortisol is measured using a specialized immunoassay method that detects free (unbound) cortisol in your serum. This test helps avoid interference from other proteins in the blood.
Can diet or medications affect cortisol test results?
Yes, certain medications (like steroids) or dietary factors (e.g., caffeine, alcohol) may influence cortisol levels. Your doctor will consider these factors when interpreting your results.
  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