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Serum/Plasma Free Cortisol by High-Performance Liquid Chromatography (HPLC)

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

This test measures the amount of cortisol (a hormone produced by your adrenal glands) that is not bound to proteins in your blood, helping assess cortisol levels in your body.

Quick summary

["Free cortisol helps 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
56501-0
Short code
GH 6h p chal SerPl-mCnc
Synonyms
GH 6h p chal 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 hormonal imbalances, such as an overproduction or underproduction of cortisol. It can also be used to monitor conditions like Cushing’s disease or Addison’s disease. Free cortisol testing helps distinguish between different causes of elevated or low cortisol levels, as cortisol bound to proteins may not reflect true biological activity.

What to Expect Before the Test

No special preparation is needed for this test. You may have a blood draw in a clinic or lab. If you’re taking medications that affect cortisol levels (like steroids), your doctor may instruct you to stop them temporarily or adjust your timing.

What the Test Results Mean

Results are compared to reference ranges for free cortisol in serum/plasma. Abnormally high or low levels may indicate hormonal disorders, infections, or other health issues. Your doctor will interpret the results in the context of your medical history and other tests.

Common Conditions Linked to Free Cortisol

High free cortisol levels may suggest conditions like Cushing’s syndrome (excess cortisol from the adrenal glands or pituitary), while low levels could indicate adrenal insufficiency (Addison’s disease) or other causes of cortisol deficiency. Chronic stress or certain medications can also influence cortisol levels.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Cortisol

Frequently asked questions

What causes abnormal free cortisol levels?
Abnormal free cortisol levels can result from hormonal disorders (e.g., Cushing’s syndrome, Addison’s disease), prolonged stress, certain medications (like steroids), or even thyroid conditions. If you experience symptoms like weight changes, fatigue, or mood swings, discuss these with your doctor.
How is this test different from a total cortisol test?
Free cortisol measures only the hormone that’s not bound to proteins, while total cortisol includes both free and protein-bound cortisol. This distinction helps doctors better understand whether cortisol is being produced in excess or deficiently, especially in conditions like Cushing’s syndrome or adrenal insufficiency.
Can diet or medications affect free cortisol levels?
Yes, certain foods, caffeine, and medications (including steroids) can temporarily alter cortisol levels. If you’re taking medications or have dietary restrictions, your doctor may recommend timing your test or adjusting your routine to get the most 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 16, 2026. · Read our editorial policy