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Cortisol, Serum (Free)

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

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

Quick summary

["Free cortisol levels help diagnose conditions like Cushing’s syndrome or adrenal insufficiency."]

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

Key facts at a glance

LOINC
48103-6
Short code
Cortis 4 AM specimen SerPl-sCnc
Synonyms
Cortis 4 AM specimen SerPl-sCnc
Category
hormone
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
0
Ref high
17
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 a free cortisol test to check for hormonal imbalances, such as whether your body is producing too much or too little cortisol. It can also help evaluate conditions like adrenal tumors, pituitary disorders, or reactions to stress or medications.

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 your doctor specifies it. Bring any medications you’re taking, as some may affect results.

How the Test Works

A blood sample is drawn from a vein in your arm. The sample is processed to isolate free cortisol, which is then measured using a sensitive immunoassay method to detect its presence.

What the Results Mean

Results are compared to reference ranges for your age and health status. Abnormally high or low levels may signal underlying conditions requiring further medical evaluation.

Reference range

NCBI: NSE 0-17 ng/mLN/A

Specimen: serum

No special preparation usually required. Stay well hydrated. Inform your healthcare provider of all medications and supplements you are taking.

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 high results may occur due to recent stress, certain medications (e.g., steroids), or improper sample handling. False low results could result from fasting errors, lab errors, or conditions like severe illness. Always discuss results with your doctor.
How often should I get this test?
Your doctor will determine the frequency based on your symptoms, medical history, and test results. Follow-up testing may be needed if initial results are abnormal or if you’re managing a known condition.
Can diet or exercise affect cortisol levels?
Yes, stress (physical or emotional), poor sleep, and certain medications can temporarily alter cortisol levels. Avoiding caffeine, alcohol, or intense exercise before testing may help ensure more accurate 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