Serum or plasma concentration of free (unbound) testosterone
This test measures the amount of free testosterone in your blood, which is the form of the hormone that actively circulates in your body. Free testosterone is important for hormone balance, muscle mass, and overall health.
["Understanding your free testosterone levels helps assess hormone health and potential deficiencies or imbalances."]
Key facts at a glance
- LOINC
- 39931-1
- Short code
- NM Hrt Gated+WM+EF W RNC IV
- Synonyms
- NM Hrt Gated+WM+EF W RNC IV
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- nm
- 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 Free Testosterone Matters
Free testosterone is the biologically active form of testosterone that isn’t bound to proteins in your blood. It plays a key role in maintaining muscle strength, bone density, and sexual function. Unlike total testosterone, free testosterone reflects the hormone’s availability for use by your body’s tissues.
How It’s Used in Healthcare
Doctors may order a free testosterone test to diagnose conditions like hypogonadism (low testosterone), polycystic ovary syndrome (PCOS), or to monitor treatment for hormone-related disorders. It can also help differentiate between total and free testosterone when evaluating symptoms.
Sample Collection and Preparation
This test requires a blood sample drawn from a vein, typically in the arm. The sample is collected in a tube that separates serum (liquid part after clotting) or plasma (liquid part after anticoagulation). Free testosterone is measured after extracting it from the blood sample using specialized techniques.
What to Expect Before the Test
No special preparation is usually needed, but you may be asked to avoid certain medications (like some steroids) that could affect hormone levels. If you’re pregnant or breastfeeding, let your healthcare provider know before testing.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
Free testosterone level
Frequently asked questions
What causes free testosterone levels to be low?
How long does it take to get the results?
Can diet or exercise affect free testosterone levels?
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