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Cortisol, Free (Serum or Plasma)

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

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

Quick summary

["Assesses your body’s cortisol levels for 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
32314-7
Short code
Cortis 1.5h p chal SerPl-sCnc
Synonyms
Cortis 1.5h p chal SerPl-sCnc
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 Matters

Your doctor may order a free cortisol test to diagnose or monitor conditions affecting your adrenal glands or pituitary hormone balance. Free cortisol is more accurate than total cortisol because it reflects the biologically active form of the hormone.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8 hours before the test if your provider specifies it. Bring a list of medications you’re currently taking, as some can affect results.

How the Test Works

A blood sample is drawn from a vein in your arm. The sample is processed to measure free cortisol levels using a sensitive laboratory method, often immunoassay or chemiluminescent immunoassay, to detect small amounts accurately.

Possible Results and Next Steps

Results may be compared to your baseline or to reference ranges provided by your lab. Elevated or low levels can signal underlying health issues that require further evaluation, such as additional hormone tests or imaging.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Cortisol’s Role and Implications

Short name

Free Cortisol

Frequently asked questions

What does a high cortisol level mean?
High free cortisol levels may indicate Cushing’s syndrome (overactive adrenal glands), prolonged stress, or certain medications that increase cortisol production. Your doctor may recommend further testing, like a 24-hour urine cortisol test or dexamethasone suppression test, to confirm the diagnosis.
What does a low cortisol level mean?
Low free cortisol can signal adrenal insufficiency (Addison’s disease) or pituitary disorders that disrupt cortisol production. Symptoms like fatigue, weight loss, or salt cravings may also prompt further evaluation, including cortisol stimulation tests or adrenal antibody checks.
Does diet or medications affect this test?
Yes, certain foods, supplements, or medications (e.g., steroids, some antidepressants) can influence cortisol levels. Always inform your healthcare provider about all medications, including over-the-counter drugs and herbal products, to avoid misleading 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