Free Testosterone (Serum)
This test measures the amount of free (unbound) testosterone in your blood, which is the form that actively influences hormones and health.
["Free testosterone helps balance hormones and may affect energy, mood, and reproductive health."]
Key facts at a glance
- LOINC
- 25987-9
- Short code
- Testost Free SerPl RIA-sCnc
- Synonyms
- Testost Free SerPl RIA-sCnc
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- ria
- 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 doctor may order this test to check for hormonal imbalances, especially if you have symptoms like low libido, irregular periods, fatigue, or signs of androgen deficiency (in men) or estrogen dominance (in women). It can also help diagnose conditions like polycystic ovary syndrome (PCOS) or evaluate hormone replacement therapy.
What Does It Measure?
Free testosterone is the portion of total testosterone that is not bound to proteins (like sex hormone-binding globulin) and is therefore biologically active. Unlike total testosterone, free testosterone reflects the hormone’s true impact on your body’s systems.
Sample Collection and Preparation
A blood sample is taken from a vein in your arm. The sample is collected in a special tube to separate serum (the liquid part after clotting) for testing. Free testosterone is measured using a sensitive immunoassay method to detect its concentration accurately.
What to Expect Before the Test
No special preparation is needed, but avoid taking certain medications (like some birth control pills or hormone therapies) that could affect results. If you’re on long-term steroids or other hormonal treatments, let your doctor know.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
Free testosterone
Frequently asked questions
Low free testosterone levels may indicate conditions like hypogonadism (low testosterone production), adrenal insufficiency, or liver disease. High levels could suggest androgen excess, Cushing’s syndrome, or tumors producing excess hormones. Monitoring free testosterone helps guide treatment for hormonal disorders or fertility planning.
Results are typically available within 1 to 3 business days, depending on your lab’s processing time. Your doctor will discuss the findings with you during your follow-up visit.
What if my results are outside the expected range?
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