Laboratory Assessment of Testicular Function

Since the symptoms of hypogonadism are nonspecific, and the signs of testosterone deficiency can be subtle and slow to develop, the assessment of testicular function relies heavily on laboratory testing. The laboratory diagnosis of hypogonadism is based on a consistent and unequivocally low serum total testosterone level measured in blood samples obtained in the early morning, but normal ranges vary with different methods and among laboratories. Moreover, many men who present with adult onset testosterone deficiency have a low level of sex hormone-binding globulin (SHBG) associated with obesity, insulin resistance, and type 2 diabetes. In these men, tests for the free (or non-SHBG/bioavailable) testosterone fraction testosterone) are helpful for an accurate diagnosis. If testosterone deficiency is confirmed, the next step is to differentiate between primary and secondary hypogonadism by measuring LH and FSH. With many disorders, however, both the testes and the hypothalamic-pituitary unit are affected. Other tests such as estradiol, inhibin-B, and Mullerian inhibitory hormone, and provocative endocrine tests using hCG, GnRH or its analogs, or antiandrogens or antiestrogens, and semen analysis in the subfertile male are discussed. For complete coverage of all related areas of Endocrinology, please visit our on-line FREE web-text, WWW.ENDOTEXT.ORG.