Cortisol, Free (Serum or Plasma)
This test measures the amount of cortisol, a natural steroid hormone produced by your adrenal glands, in your blood. Free cortisol means the hormone is unbound to proteins and available to affect your body.
["Your doctor may check free cortisol levels to diagnose or monitor conditions affecting hormone balance."]
Key facts at a glance
- LOINC
- 1436-5
- Short code
- Cortis 8h p 30 mg/kg MTP PO SerPl-mCnc
- Synonyms
- Cortis 8h p 30 mg/kg MTP PO SerPl-mCnc
- Category
- hormone
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 8
- Ref high
- 61
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 82977
- 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 healthcare provider might order a free cortisol test to evaluate adrenal gland function, check for conditions like Cushing’s syndrome (too much cortisol), or rule out adrenal insufficiency (too little cortisol). It can also help diagnose issues like pituitary tumors or other hormonal imbalances.
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 urine collection. If drawn from serum/plasma, you’ll lie down for comfort, and a small needle will be used to collect blood.
What the Test Results Mean
Results are compared to general reference ranges for free cortisol in serum/plasma, but your doctor will interpret them in the context of your symptoms, medical history, and other tests. Abnormal results may trigger further evaluation.
Common Conditions Affecting Results
Cortisol levels can be influenced by stress, medications (like steroids), certain medications (e.g., birth control), or time of day. Chronic stress or recent illness may temporarily alter results.
Reference range
Adult males: 8-61 U/L; Adult females: 5-36 U/LN/A
No special preparation usually required. Stay well hydrated. Inform your healthcare provider of all medications and supplements you are taking.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance
Short name
Free Cortisol
Frequently asked questions
What causes high cortisol levels?
What causes low cortisol levels?
How often should I get this test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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