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Cortisol in Plasma (Free Cortisol)

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

This test measures the amount of free cortisol, a hormone produced by your adrenal glands, in your blood plasma. Free cortisol is the active form of cortisol that circulates freely in your bloodstream.

Quick summary

["Free cortisol helps regulate metabolism, immune response, and stress reactions."]

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

Key facts at a glance

LOINC
58624-8
Short code
ACTH pre Glc Plas-mCnc
Synonyms
ACTH pre Glc Plas-mCnc
Category
glucose
Sample
plasma
Container
Lavender-top (EDTA) or Green-top (Heparin)
Units
N/A
Ref low
10
Ref high
60
Fasting
true
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 evaluate adrenal gland function, diagnose conditions like Cushing’s syndrome or adrenal insufficiency, or assess how your body responds to stress or medications that affect cortisol levels.

What to Expect Before the Test

No special preparation is usually needed, but your doctor might instruct you to avoid certain medications or activities (like smoking or caffeine) for a few days before testing. You’ll provide a blood sample drawn from a vein in your arm.

How the Test Works

Blood is collected and processed to separate plasma from blood cells. The free cortisol in the plasma is then measured using a sensitive immunoassay technique to detect its presence.

Possible Results and Interpretation

Results are compared to reference ranges specific to your age, sex, and health status. Abnormally high or low levels may signal underlying medical conditions requiring further evaluation.

Reference range

NCBI: ACTH 10-60 pg/mLN/A

Specimen: plasma

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.

◆Associated findings1

Short name

Free Cortisol

Frequently asked questions

What causes elevated cortisol levels?
Elevated cortisol can result from conditions like Cushing’s syndrome (due to excess hormone production), prolonged stress, certain medications, or tumors affecting the adrenal glands or pituitary.
What causes low cortisol levels?
Low cortisol levels may occur with adrenal insufficiency (e.g., Addison’s disease), sudden withdrawal from cortisol-replacement medications, or severe illness or trauma that temporarily disrupts adrenal function.
How often should I get this test?
Your doctor will determine how often this test is needed based on your symptoms, medical history, and treatment plan. Regular follow-ups may be scheduled if you have chronic conditions like adrenal disorders.
  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