Serum/plasma mass concentration of free cortisol
This test measures the amount of free (unbound) cortisol in your blood, which is important for assessing cortisol function and diagnosing conditions like Cushing’s syndrome or adrenal insufficiency.
["Free cortisol helps evaluate hormone balance and potential adrenal or pituitary disorders."]
Key facts at a glance
- LOINC
- 47924-6
- Short code
- GH 5M p Arg SerPl-aCnc
- Synonyms
- GH 5M p Arg SerPl-aCnc
- 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 is this test done, and what can your doctor learn about your health by measuring free cortisol levels?
Your healthcare provider may order this test to check for conditions affecting cortisol production, such as Cushing’s disease (too much cortisol) or adrenal insufficiency (too little cortisol). It may also be used to monitor treatment responses or rule out other hormonal imbalances.
What does your test result mean, and how do doctors interpret high or low free cortisol values in your lab report?
Results are not provided with specific reference ranges. Interpretation depends on clinical context, including symptoms, other test results, and medical history. High or low levels may signal underlying health issues that need further evaluation.
How is the sample collected and how should you prepare, including the steps and instructions to follow before testing?
A blood sample is drawn from a vein, usually in a clinic or lab. The sample is collected in a special tube to separate serum or plasma, which is then sent for analysis. Avoiding stress or caffeine before the test may help ensure accurate results.
What can you expect before the test, from scheduling your appointment to any guidance your healthcare team may give you?
No special preparation is typically required, but inform your provider about medications (especially steroids), recent stress, or illness. If you’re pregnant, breastfeeding, or have certain conditions, discuss this with your doctor.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance
Short name
Free Cortisol Level
Frequently asked questions
Free cortisol testing is critical for diagnosing conditions like Cushing’s syndrome (excess cortisol) or adrenal insufficiency (low cortisol). It helps differentiate between primary and secondary causes of hormonal disorders and guides treatment decisions.
This test uses a mass concentration method (likely liquid chromatography-mass spectrometry or a similar advanced technique) to detect cortisol in its unbound (free) form, ensuring accurate reflection of active hormone levels in your blood.
Yes, cortisol levels can fluctuate with stress, physical activity, sleep, and certain medications. Avoiding high-stress situations or caffeine before testing may help stabilize results.
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