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Cortisol (Serum or Plasma) with Free Cortisol Measurement

Published: August 9, 2026Updated: August 16, 2026

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

Quick summary

["Free cortisol helps assess adrenal function and potential hormone imbalances."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
101979-3
Short code
Cortsol p argi pnl SerPl
Synonyms
Cortsol p argi pnl SerPl
Category
hormone
Sample
serum
Container
Red-top tube (SST)
Units
N/A
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 This Test Might Be Ordered

Your doctor may recommend this test if you have symptoms like unexplained fatigue, weight changes, high blood pressure, or signs of adrenal insufficiency or excess (e.g., Cushing’s syndrome). It can also help diagnose conditions like Addison’s disease or evaluate stress-related hormone levels.

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 doctor know.

What the Results Mean

Results are compared to standard ranges for your age and sex. Abnormal levels may indicate issues with your adrenal glands, stress responses, or other hormonal imbalances.

Common Conditions This Test Helps Diagnose

This test is often used to diagnose or monitor conditions like Cushing’s syndrome, adrenal insufficiency (Addison’s disease), or to evaluate cortisol levels during stress (e.g., in critical care settings).

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Cortisol

Frequently asked questions

What does ‘free cortisol’ mean in this test?
'Free cortisol' refers to the cortisol molecule that is unbound to proteins in your blood. Only this fraction is biologically active and can cross cell membranes to exert its effects, so measuring it provides a more accurate picture of your body’s active hormone levels.
Can food or medications affect cortisol test results?
Certain medications (like steroids, beta-blockers, or some antidepressants) can influence cortisol levels. Eating a balanced meal before the test may help stabilize blood sugar, but avoid caffeine or alcohol for 24 hours before testing, as they can temporarily alter cortisol.
Is this test painful?
The blood draw itself causes mild discomfort for a few seconds, but most people tolerate it well. The needle is small, and you may feel a slight pinch. If you’re anxious, let your healthcare provider know to use a larger gauge needle or apply a numbing cream.
  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 16, 2026. · Read our editorial policy