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Cortisol, Serum Free (Mass Concentration)

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

This test measures the amount of free cortisol, a hormone produced by your adrenal glands, in your blood. Free cortisol is the active form that circulates freely in your serum.

Quick summary

["Free cortisol levels help 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
26530-6
Short code
Cortis 30M p ACTH SerPl-mCnc
Synonyms
Cortis 30M p ACTH 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 healthcare provider may order this test to evaluate conditions like Cushing’s syndrome (too much cortisol), adrenal insufficiency (too little cortisol), or to monitor treatment for hormone-related disorders. It can also help diagnose issues like pituitary tumors or stress-related hormone changes.

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 cortisol levels are measured at specific times (e.g., morning or evening). Blood is drawn from a vein in your arm.

What Happens During the Test?

A healthcare professional will insert a small needle into your arm to draw blood. You may feel a slight pinch, but it usually takes only a few minutes. The blood sample is then sent to a lab for analysis.

What Are the Results?

Results are typically reported as a mass concentration of cortisol in your serum. Your provider will compare these results to your clinical picture and other tests to determine if further action is needed.

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 does a high or low free cortisol level mean?
High free cortisol levels may suggest conditions like Cushing’s syndrome, where the body produces too much cortisol, or certain medications that affect cortisol metabolism. Low levels could indicate adrenal insufficiency, where the adrenal glands don’t produce enough cortisol, or conditions affecting the pituitary gland.
How often will I need this test?
The frequency depends on your medical condition and treatment plan. Your healthcare provider will determine how often you need follow-up tests based on your symptoms and lab results.
Can I eat or drink before this test?
If fasting is required, avoid food and liquids (except water) for 8–12 hours before the test. If no fasting is needed, you can eat and drink normally, but check with your provider for specific instructions.
  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