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Cortisol, Free Serum

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

This test measures the amount of free cortisol, a form of the hormone cortisol that circulates freely in your blood. Free cortisol is important for regulating metabolism, immune response, and stress reactions.

Quick summary

["Free cortisol helps your body manage stress and maintain balance in key bodily functions."]

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

Key facts at a glance

LOINC
66764-2
Short code
nRBC BldCo-Rto
Synonyms
nRBC BldCo-Rto
Category
chemistry
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Ref low
4.2
Ref high
5.9
Critical range
2 N/A – 7 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
85041
SNOMED
900000000000003001
Specimen volume
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
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 fatigue, weight changes, or mood swings that could be linked to hormonal imbalances. It’s also used to diagnose conditions such as Cushing’s syndrome, adrenal insufficiency, or to monitor treatment for hormone-related disorders.

What to Expect Before the Test

No special preparation is needed for this test. You’ll have a small needle inserted into your arm to draw blood. If you’re taking medications that affect cortisol levels (like steroids), let your provider know before the test.

What the Results Mean

Free cortisol levels can vary based on when the blood sample is taken. Results are typically compared to reference ranges for your age and health status. Abnormal results may require further testing or evaluation by a specialist.

Common Conditions Linked to Free Cortisol

High free cortisol levels may indicate conditions like Cushing’s syndrome, where the body produces too much cortisol. Low levels might suggest adrenal insufficiency or other hormonal disorders that need medical attention.

Reference range

Adult males: 4.2-5.9; Females: 3.8-5.1 x 10^12/LN/A

Specimen: whole-blood

No special preparation required. Stay well hydrated.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Cortisol

Frequently asked questions

Why might my cortisol levels be checked during pregnancy?
Free cortisol is sometimes measured during pregnancy to check for conditions like gestational diabetes or other hormonal imbalances that could affect your health or your baby’s. It’s also important for monitoring stress-related symptoms or diagnosing rare disorders.
What if my cortisol test comes back abnormal?
If your results are outside the expected range, your healthcare provider will discuss next steps, which may include additional tests, lifestyle adjustments, or referring you to a specialist like an endocrinologist. They’ll work with you to understand the cause and develop a treatment plan.
Does diet or stress affect cortisol levels?
Yes, both diet and stress can influence cortisol levels. Eating a balanced diet, managing stress through techniques like exercise or relaxation, and avoiding excessive caffeine or alcohol may help support healthy cortisol levels. Always follow your provider’s advice for managing any underlying 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 17, 2026. · Read our editorial policy