There are two main types of hypogonadism: primary (or testicular) and secondary (or hypothalamic-pituitary) hypogonadism.
Primary hypogonadism is characterized by low testosterone levels, impairment of spermatogenesis, and elevated levels of gonadotrophins, which can be due to a genetic cause (e.g. Klinefelter’s syndrome, in which males have an extra X sex chromosome) or to damage to the testes (such as injury or infection).
Secondary hypogonadism is characterized by low testosterone levels in association with low or low-normal gonadotrophin levels, and may result from conditions such as Kallmann syndrome, characterized by insufficient production of gonadotrophin-releasing hormone by hypothalamus, leading to a deficiency in the production of luteinizing hormone and follicle-stimulating hormone by the pituitary.1
1. Bhasin S, Cunningham GR, Hayes FJ, et al. Testosterone therapy in adult men with androgen deficiency syndromes: an endocrine society clinical practice guideline. J Clin Endocrinol Metab 2006; 91(6): 1995-2010