Free testosterone
HormonesThe unbound, biologically active fraction of total testosterone that can interact with cellular receptors.
This measurement provides insight into androgenic activity affecting metabolism, body composition, and various physiological functions.
Why this matters
Free testosterone levels provide insight into hormone activity beyond total testosterone. Low free testosterone can impair strength, bone health, and sexual function even if total testosterone is normal. Lifestyle factors such as weight management, exercise, and sleep help maintain healthy free testosterone levels.
How this connects to other biomarkers
- Free Testosterone is the biologically active fraction — it can be low even when Testosteron, total is normal, if Sex hormone-binding globulin (SHBG) is high (overactive thyroid, oral estrogen, liver disease).
- Low free Testosterone with symptoms warrants distinguishing primary (high Luteinizing hormone (Lutropin) / FSH, Follitropin) from secondary (low gonadotropins) low testosterone.
- In women, elevated free Testosterone with low SHBG and high Free Androgen Index (FAI) points to PCOS (polycystic ovary syndrome) or other androgen excess.
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