Serum and blood testing is done to determine the availability of testosterone and levels of leutenizing and gonadotropin-releasing hormones in the body. Men with low testosterone in whom normal or high gonadotropin levels are found typically have primary testosterone deficiency, which stems from a problem in the testicles.
Secondary and tertiary types, caused by problems of the hypothalamus or pituitary gland, often result in low testosterone and low gonadotropin levels.
Other tests involve injecoting GnRH or clmiphene citrate (an estrogen) to stimulate a diagnostic response within the hypothalamic-pituitary gonadal axis.
Rarely, testicular biopsy is done, usually in cases where sperm is absent from ejaculate despite normal testicle development. Biopsy, which involves using a needle to collect a sample of testicular tissue, may detect a malfunction in sperm production.