What is primary vs secondary hypogonadism?

Hypogonadism, or low testosterone, stems from two distinct physiological origins. In primary hypogonadism, the testes themselves fail to produce adequate testosterone, despite receiving normal hormonal signals from the brain. Causes include aging, injury, undescended testicles, genetic conditions, or previous chemotherapy. Blood tests show low testosterone paired with elevated luteinizing hormone (LH), reflecting the body's attempt to stimulate failing testes.

Secondary hypogonadism occurs when the pituitary gland or hypothalamus (the brain structures that regulate testosterone production) do not send sufficient signaling hormones to the testes. The testes themselves are capable of producing testosterone, but lack the chemical trigger to do so. Common causes include pituitary tumors, head injury, obesity, sleep apnea, and certain medications. Blood tests show low testosterone alongside low or normal LH levels.

This distinction matters because treatment pathways differ. Primary hypogonadism typically requires testosterone replacement therapy, as the testes cannot recover function on their own. Secondary hypogonadism may respond to medications that stimulate the pituitary (such as gonadotropin-releasing hormone agonists), though testosterone replacement is also an option. Accurate diagnosis through blood work and sometimes imaging is essential before starting treatment. If you need guidance determining which type you may have, consult providers specializing in endocrinology to ensure proper evaluation.