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Cortisol, Free (Serum/Plasma)

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

This test measures the amount of free cortisol, a hormone produced by your adrenal glands that helps regulate metabolism, immune response, and stress reactions.

Quick summary

["Free cortisol helps 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
9615-6
Short code
Cortis 1.5h p 250 ug ACTH IM SerPl-mCnc
Synonyms
Cortis 1.5h p 250 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 diagnose or monitor conditions like Cushing’s syndrome (overactive adrenal glands), adrenal insufficiency (underactive adrenal glands), or to check for cortisol-related issues before certain treatments.

What to Expect Before the Test

No special preparation is needed, but if you’re taking medications that affect cortisol levels (like steroids), your doctor may ask you to stop them temporarily or adjust timing.

How the Test Is Performed

A blood sample is drawn from a vein in your arm. You may feel a slight pinch, but it usually doesn’t cause discomfort. The sample is sent to a lab for analysis using a sensitive immunoassay method.

What the Results Mean

Results are compared to general reference ranges for free cortisol in serum/plasma. Abnormal levels may indicate hormonal imbalances or other health concerns that need 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. Elevated cortisol can signal conditions like Cushing’s syndrome, while low levels may point to adrenal insufficiency or other endocrine disorders. Your doctor will interpret results in the context of your symptoms and medical history.

Short name

Free Cortisol

Frequently asked questions

What causes false high or low cortisol results?
False results can occur if you didn’t follow preparation instructions (e.g., missed medications), had recent stress, or had a recent illness. Your doctor may recommend repeat testing if initial results seem unclear.
How often should I get this test?
Frequency depends on your condition. Some patients need testing monthly, while others may only need it once or twice a year. Follow your doctor’s plan.
Can diet or exercise affect cortisol levels?
Yes, extreme stress, poor sleep, or certain foods (like caffeine) can temporarily raise cortisol. Avoiding these factors before testing may improve accuracy.
  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