What is follicle stimulating hormone (FSH)?
Follicle stimulating hormone (FSH) is a pituitary gland hormone that directly regulates spermatogenesis and testicular function in men. It is measured alongside LH and testosterone in baseline and monitoring hormone panels for TRT candidates.
FSH, produced by the anterior pituitary gland, plays a central role in male reproductive function by stimulating Sertoli cells within the seminiferous tubules of the testes to support spermatogenesis, the process of sperm cell development. Unlike testosterone, which affects secondary sexual characteristics and general male function, FSH directly controls the quantity and quality of sperm production.
In men seeking testosterone replacement therapy or presenting with symptoms of low testosterone, FSH levels reveal important information about baseline testicular function and the hypothalamic-pituitary-testicular (HPT) axis. Low FSH paired with low testosterone suggests central hypogonadism (a pituitary or hypothalamic issue), while low testosterone with normal or elevated FSH indicates primary testicular failure. This distinction affects both diagnosis and treatment approach.
FSH is routinely tested alongside luteinizing hormone (LH) and testosterone as part of comprehensive hormone panels during TRT evaluation. Clinics use these three markers together to assess whether low testosterone symptoms stem from the testes themselves or from signaling problems upstream in the pituitary. Monitoring FSH during treatment also helps determine whether exogenous testosterone is suppressing natural hormone production and fertility. Providers offering diagnostic services and lab work typically include FSH in their standard hormone panels for this reason.