Skip to content

Serum or plasma mass concentration of free (unbound) cortisol

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

This test measures the amount of cortisol that is not attached to proteins in your blood, which can help assess how well your body is producing cortisol or if there are issues with how it’s used by your body.

Quick summary

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

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

Key facts at a glance

LOINC
56885-7
Short code
GH 3h P Exc SerPl-mCnc
Synonyms
GH 3h P Exc SerPl-mCnc
Category
chemistry
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 Is Done

Your doctor may order this test if they suspect conditions affecting cortisol production, such as Cushing’s disease (too much cortisol) or adrenal insufficiency (too little cortisol). It can also be used to monitor treatment for these conditions or evaluate symptoms like fatigue, weight changes, or unexplained high blood pressure.

How the Test Works

Blood is drawn from a vein, usually in your arm. The sample is then processed to separate free cortisol from protein-bound cortisol. The free cortisol concentration is measured using a specialized laboratory technique.

What to Expect Before the Test

No special preparation is typically needed, but you may be asked to avoid certain medications or supplements that could affect cortisol levels, such as steroids or some herbal products. Stressful events or physical activity can also temporarily influence results.

What to Expect During the Test

The blood draw is quick and usually painless. You may feel a slight pinch, but most people tolerate it well. You can resume normal activities immediately afterward.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Cortisol

Frequently asked questions

How is this test different from total cortisol?
Free cortisol is measured separately from protein-bound cortisol, giving a more accurate reflection of biologically active cortisol in your blood. Total cortisol includes both free and bound forms, so it may not always reflect true physiological activity.
Does fasting affect this test?
Fasting may not significantly alter free cortisol levels, but stress, exercise, or certain medications can. Your doctor may recommend avoiding these factors if they suspect a specific condition.
Can I take my usual medications before this test?
Some medications, like steroids or certain supplements, may affect cortisol levels. Always inform your doctor about all medications or supplements you’re taking before the test.
  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