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Cortisol, Free (Serum or Plasma)

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

This test measures the amount of free cortisol, the active form of the hormone cortisol, in your blood. Free cortisol is not bound to proteins and is available to affect your body’s response to stress, blood pressure, and other functions.

Quick summary

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

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

Key facts at a glance

LOINC
49968-1
Short code
Cortis 1h p 250 ug ACTH IM SerPl-SCDiff
Synonyms
Cortis 1h p 250 ug ACTH IM SerPl-SCDiff
Category
hormone
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
60
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 healthcare provider may recommend this test if you have symptoms like unexplained weight changes, fatigue, or signs of adrenal gland issues (such as high or low blood pressure, salt cravings, or frequent infections). It could also be used to diagnose conditions like Cushing’s syndrome, adrenal insufficiency, or other hormonal disorders.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the test if it’s part of a 24-hour cortisol collection. If you’re taking medications that affect cortisol levels, let your provider know. Blood is drawn from a vein in your arm.

What the Test Results Mean

Free cortisol levels can vary based on your time of day, stress levels, and overall health. Your results will be compared to standard reference ranges provided by your lab. Abnormal results may prompt further testing or evaluation by your doctor.

Common Conditions This Test Helps Diagnose

This test helps identify conditions such as Cushing’s syndrome (high cortisol), adrenal insufficiency (low cortisol), or other hormonal imbalances. It may also be used to monitor treatment for conditions affecting cortisol production or metabolism.

Reference range

NCBI: ACTH 10-60 pg/mLN/A

Specimen: serum

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.

Clinical Significance: Cortisol’s Role and When It Matters

Short name

Free Cortisol

Frequently asked questions

What are the normal ranges for free cortisol in blood?
Normal ranges can vary by lab and testing method. Your specific reference ranges will be provided with your results. Free cortisol is highest in the morning and lowest at night, so timing matters. If your results are outside the expected range, your doctor may recommend additional testing, such as a 24-hour urine cortisol collection or a dexamethasone suppression test.
Why might my doctor order a free cortisol test?
Your doctor may order this test if you have symptoms like persistent fatigue, unexplained weight gain or loss, high blood pressure, or frequent infections. It can also help diagnose conditions like Cushing’s disease (caused by a pituitary tumor) or adrenal gland disorders. If you’ve recently been diagnosed with a hormonal condition, this test may be part of ongoing monitoring.
Can stress affect my cortisol levels?
Yes, stress—whether physical, emotional, or from illness—can temporarily raise cortisol levels. If you’re under significant stress before your test, let your healthcare provider know, as this may impact results. Avoiding extreme stress for a few days before testing can help ensure more 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 17, 2026. · Read our editorial policy