Testosterone, Free (Serum/Plasma)
This test measures the amount of free (unbound) testosterone in your blood. Free testosterone is the active form of the hormone that your body uses.
["Free testosterone reflects your biologically available hormone levels."]
Key facts at a glance
- LOINC
- 17690-9
- Short code
- Testost 2h p chal SerPl-mCnc
- Synonyms
- Testost 2h p chal SerPl-mCnc
- 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?
Your healthcare provider may order a free testosterone test to evaluate hormone balance, especially if you have symptoms related to low or high testosterone levels, such as fatigue, changes in mood, or reproductive issues. It can also help diagnose conditions like hypogonadism (low testosterone) or Cushing’s syndrome (high cortisol-related testosterone changes).
What does the test involve?
A blood sample is taken from a vein in your arm. The sample is then processed to measure the free (non-protein-bound) testosterone concentration in your serum or plasma.
What should you do before the test?
Avoid smoking and consuming alcohol for at least 24 hours before the test. Wear comfortable clothing and fast if instructed, as fasting may be required depending on your specific test protocol.
What might affect the results?
Certain medications, such as steroids or hormonal therapies, can influence testosterone levels. Stress, illness, or recent exercise may also temporarily affect results. Always inform your provider about all medications or supplements you take.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Free testosterone levels help assess whether your body is producing enough of this hormone to support normal function. Low free testosterone can cause symptoms like low libido, muscle weakness, or mood changes, while high levels may indicate conditions like polycystic ovary syndrome (PCOS) or tumors. This test is particularly useful for diagnosing hormone-related disorders in both men and women.
Short name
Free testosterone
Frequently asked questions
How is this test different from total testosterone?
Will I need to prepare differently for this test than other blood tests?
Can free testosterone levels change over time?
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