Free testosterone represents the small fraction (~1–3%) of total testosterone that is unbound and biologically active.

It directly influences sexual function, muscle mass, bone density, mood, and energy levels.

Clinical uses include:

Diagnosing hypogonadism when total testosterone levels are borderline.

Evaluating male infertility, erectile dysfunction, and decreased libido.

Assessing polycystic ovary syndrome (PCOS) and hyperandrogenism in women.

Monitoring hormone replacement therapy.

Often performed alongside Total Testosterone, SHBG, LH, and FSH tests for a complete hormonal profile.

Analyte: Free Testosterone in serum (pg/mL).

Normal Range (varies by lab):

Adult men: ~5–25 pg/mL

Adult women: ~0.3–1.9 pg/mL

Abnormal Findings:

Low free testosterone: Hypogonadism, pituitary/hypothalamic dysfunction, chronic illness, certain medications.

High free testosterone: PCOS, androgen‑secreting tumors, anabolic steroid use.

Clinical Use:

Provides a direct measure of biologically active testosterone.

Helps guide diagnosis and management of reproductive and endocrine disorders.

Supports urology, endocrinology, and gynecology evaluations.