A Free Testosterone test measures the amount of testosterone in your blood that is unbound (also called free testosterone or unbound testosterone). This is the portion of testosterone that is not attached to carrier proteins—mainly sex hormone–binding globulin (SHBG) and albumin. Because free testosterone can enter cells more easily, it is often considered the most bioactive testosterone—the form most closely linked to symptoms.

Testosterone circulates in three main forms:

• Bound to SHBG (tightly bound; usually not available to tissues)
• Bound to albumin (loosely bound; can be available to tissues)
• Free (unbound) (the smallest fraction, but highly active)

Many people first have a total testosterone test. However, total testosterone can look “normal” even when the biologically available portion is low, especially if SHBG is high. That’s why a free testosterone measurement (or a calculated estimate using total testosterone, SHBG, and albumin) can provide deeper insight when total testosterone is borderline or doesn’t match symptoms.

In plain language: A low free testosterone level may help explain symptoms such as low sex drive, erectile dysfunction, fatigue, mood changes, reduced muscle mass, or irregular periods—even if total testosterone is not clearly low. A high free testosterone level may be linked with acne, excess hair growth, scalp hair thinning, or menstrual irregularity in women, and may point to testosterone overproduction or exposure to androgens. Results are interpreted based on your age, sex at birth, symptoms, time of day the blood was drawn (testosterone is often highest in the morning), and related lab results.

Clinicians commonly order a free testosterone test when they need a clearer picture of hormone activity than a total testosterone test alone can provide. It’s often used to confirm or further evaluate suspected testosterone imbalance and to help guide treatment decisions.

Your healthcare provider may recommend free testosterone testing if you have:

• Symptoms of low testosterone in men: reduced libido, erectile dysfunction, infertility, fewer morning erections, fatigue, depressed mood, irritability, decreased muscle mass/strength, increased body fat, gynecomastia (breast tissue), low bone density or fractures.
• Symptoms of excess androgens in women: acne, unwanted facial/body hair (hirsutism), scalp hair thinning, deepening voice, increased muscle mass, irregular or absent periods, difficulty getting pregnant.
• Borderline or inconsistent total testosterone results, especially when symptoms suggest a hormonal issue.
• Suspected SHBG abnormalities, since SHBG strongly affects how much testosterone is “free.” SHBG can be altered by aging, thyroid disease, liver disease, obesity/insulin resistance, pregnancy, and certain medications.
• Monitoring hormone therapy, such as testosterone replacement therapy (TRT), treatment for hypogonadism, or gender-affirming hormone therapy (testing plans vary by individual and clinician).
• Evaluation of infertility or sexual function concerns, often alongside LH, FSH, prolactin, estradiol, and semen analysis when relevant.

Because testosterone levels fluctuate, clinicians often prefer a morning blood draw (commonly between 7–10 a.m. for adult men) and may repeat testing to confirm an abnormal result before diagnosing a condition.

• Male hypogonadism (testosterone deficiency; primary or secondary)
• Polycystic ovary syndrome (PCOS)
• Androgen-secreting ovarian or adrenal tumors (rare but important to rule out when levels are very high)
• Adrenal disorders affecting androgen production (e.g., congenital adrenal hyperplasia)
• SHBG abnormalities (high or low SHBG states that can mask symptoms on total testosterone)
• Obesity and insulin resistance/metabolic syndrome (often associated with low SHBG and altered testosterone balance)
• Type 2 diabetes (may be associated with low testosterone in men and altered androgen balance)
• Thyroid disease (hyperthyroidism can raise SHBG; hypothyroidism can lower SHBG)
• Liver disease (can change SHBG production and affect measured testosterone fractions)
• Hyperprolactinemia and pituitary disorders (can suppress gonadal hormone production)

• Clarifying the cause of low libido, erectile dysfunction, or sexual wellness concerns
• Supporting fertility planning and evaluation of reproductive hormone balance
• Guiding safe, individualized management of testosterone replacement therapy (TRT) or other hormone treatments
• Tracking and improving symptoms related to energy, mood, sleep, and vitality when a hormonal issue is suspected
• Evaluating menstrual irregularity, acne, or unwanted hair growth as part of a PCOS/hyperandrogenism workup
• Monitoring hormone status in the context of metabolic health (weight management, insulin resistance) when clinically appropriate
• Assessing hormone balance when conditions that affect SHBG (thyroid or liver issues, medication effects) may be present