Male Hypogonadism

Excerpt

Ninety-five percent of the total testosterone in males is synthesized in the Leydig cells of the testes. Defects that interfere with interactions in the hypothalamic-pituitary-testicular axis can cause male hypogonadism as well as primary testicular disorders. Such defects may be acquired or congenital.

It is helpful to distinguish between primary hypogonadism (which originates in the testes) and secondary (which originates in the hypothalamus or pituitary gland). Symptoms highly suggestive of hypogonadism include decreased spontaneous erections, reduced nocturnal penile tumescence, infrequent morning erections, low libido, unexplained fatigue, and smaller testicular volume.

The normal range for early morning testosterone in a male is generally between 300 ng/dL to 1000 ng/dL, although this varies by laboratory. Hypogonadism is usually diagnosed when the morning serum testosterone level is <300 ng/dL on at least 2 occasions. Morning levels are used because testosterone levels are typically the highest. However, clinical judgment can be exercised in diagnosing hypogonadism for patients with persistent symptoms of testosterone deficiency despite having testosterone levels in the normal range.

Total testosterone <405.9 ng/dL is below the fifth percentile. Elderly males should optimally reach testosterone levels between 500 and 800 ng/dL, while young adults should expect levels between 600 and 900 ng/dL. Low testosterone levels alone do not require treatment unless they are associated with symptoms of hypogonadism.