Testosterone - Free

The Testosterone – Free test measures the small fraction of testosterone circulating in the blood without being attached to proteins. This unbound testosterone is available to enter tissues and interact with androgen receptors.

Most circulating testosterone is bound to Sex Hormone-Binding Globulin (SHBG) or albumin. Only a small percentage circulates freely. Measuring free testosterone may provide additional information when a total testosterone result does not match the patient's symptoms or when abnormal SHBG concentrations are suspected.

Testosterone is produced mainly by the testicles in males. Smaller quantities are produced by the ovaries in females and by the adrenal glands in both sexes. It contributes to reproductive function, libido, sperm production, muscle mass, bone health, body-hair development and red blood-cell production.

Benefits of the Test

• Measures the unbound fraction of circulating testosterone.
• Provides information about testosterone available to body tissues.
• Supports assessment when total testosterone does not match clinical symptoms.
• Helps evaluate suspected testosterone deficiency in males.
• Contributes to the assessment of androgen excess in females.
• May support male and female fertility evaluation.
• Can provide additional information when SHBG is unusually high or low.
• May be used to monitor selected hormone treatments.

Why Doctors Recommend This Test

A doctor may recommend free testosterone testing when symptoms suggest testosterone deficiency but total testosterone is borderline or within the laboratory reference interval. Changes in SHBG can alter total testosterone without producing an equivalent change in the free fraction.

Symptoms associated with low testosterone in adult males may include reduced sexual desire, erectile difficulties, reduced spontaneous erections, infertility, loss of muscle mass, reduced facial or body hair, breast enlargement, low bone density or unexplained anaemia. These symptoms are not specific and may have many other causes.

Free testosterone may be particularly useful when SHBG concentrations are likely to be abnormal. SHBG can be affected by ageing, obesity, insulin resistance, thyroid disorders, liver disease, certain medicines and estrogen exposure. The doctor may measure total testosterone and SHBG with free testosterone to improve interpretation.

In females, testing may be requested when symptoms suggest androgen excess. These can include excess facial or body hair, persistent acne, scalp hair thinning, irregular periods, absent periods or difficulty conceiving. Possible causes include polycystic ovary syndrome and selected ovarian, adrenal or pituitary conditions.

Free testosterone testing may also be used to monitor selected patients receiving testosterone therapy, anti-androgen treatment or gender-affirming hormone therapy. The appropriate collection time depends on the medicine, dose and route of administration.

A free testosterone result cannot independently diagnose hypogonadism, infertility or PCOS. Results must be interpreted with symptoms, total testosterone, SHBG and other relevant hormone tests.

Preparation Before Test

For adult males, morning collection is generally preferred because testosterone concentrations follow a daily rhythm and are commonly highest between approximately 7:00 AM and 10:00 AM. The doctor may request fasting to standardise the measurement.

Follow the exact preparation instructions supplied by the doctor or laboratory. If fasting is required, plain water is generally permitted unless different instructions are provided.

Inform the doctor about testosterone therapy, anabolic steroids, opioid medicines, corticosteroids, anticonvulsants, hormonal contraceptives, fertility medicines, biotin and all other medicines or supplements. These may influence testosterone concentrations, SHBG or analytical measurement.

Do not stop any prescribed medicine without medical advice. If the test is being performed to monitor hormone therapy, the doctor should determine the collection time in relation to the most recent dose.

Tell the healthcare professional about recent severe illness, insufficient sleep, strenuous exercise, major weight changes, testicular injury, pregnancy or known thyroid, liver or pituitary conditions. These factors may affect the result.

A healthcare professional collects a blood sample from a vein, usually in the arm. The method used to measure or calculate free testosterone may vary between laboratories.

Normal Reporting Time

The Free Testosterone test report is commonly available within 24–48 hours after the laboratory receives a suitable blood sample. Reporting time may vary according to the analytical method, testing schedule, laboratory workflow, quality-control checks and result verification. Specialised equilibrium-dialysis methods may require additional time.

Who Should Take This Test?

This test may be appropriate for adult males with symptoms of low testosterone, especially when total testosterone is borderline or does not explain the symptoms. It may also be requested during male infertility or pituitary and testicular function assessment.

Women may require testing for symptoms of androgen excess, such as excess facial hair, acne, scalp hair thinning, irregular periods or difficulty conceiving. Children and adolescents may occasionally be tested during specialist evaluation of early or delayed puberty.

The test may also be used to monitor selected hormone treatments. It should be performed according to medical advice and not used as a stand-alone wellness, fitness or bodybuilding assessment.

Detailed Information

Testosterone circulates in three main forms. A substantial proportion is strongly bound to SHBG, another portion is weakly bound to albumin and a small percentage remains unbound. Free testosterone refers only to the unbound fraction.

Total testosterone measures all circulating forms together. Bioavailable testosterone generally includes free testosterone plus the portion weakly bound to albumin. These terms represent different measurements and should not be treated as interchangeable.

Free testosterone may be measured directly using specialised methods such as equilibrium dialysis, or it may be estimated using total testosterone, SHBG and sometimes albumin. Different analytical approaches can produce different numerical results and reference intervals.

A low free testosterone result in a symptomatic adult male may support testosterone-deficiency assessment. However, diagnosis generally requires repeat morning testing and evaluation of the underlying cause. LH and FSH may help distinguish testicular dysfunction from reduced pituitary or hypothalamic stimulation.

An elevated free testosterone result in a woman may be associated with androgen excess. PCOS is a common cause, but ovarian and adrenal conditions, medicines and other hormonal disorders may also be considered according to the clinical presentation.

External testosterone can suppress LH and FSH and reduce sperm production. Men trying to conceive should discuss fertility goals with a specialist before beginning testosterone therapy.

Reference intervals vary according to age, sex, collection time and analytical method. Results should be interpreted using the range printed on the laboratory report and reviewed by an endocrinologist, gynaecologist, urologist, andrologist or another qualified healthcare professional.