Abstract
Testosterone affects several organs in the body and is very important for male well-being. Aging men with late-onset hypogonadism (LOH) experience physiologic, psychiatric, and sexual symptoms related to a decline in the serum concentration of testosterone with age. However, it is well-known that the extent of the decline in testosterone concentration does not correlate with the severity of LOH-related symptoms. Therefore, it is difficult to diagnose and treat patients with LOH. In addition, the symptoms, response to testosterone replacement therapy (TRT), and medical insurance coverage differ among ethnicities and countries. The evaluation of testosterone is essential for the diagnosis and treatment of LOH. The effects of testosterone are determined not only by the serum testosterone concentration but also by the androgen receptor sensitivity. A low number of glutamine repeats is indicative of high androgenic activity, and the number shows ethnicity-related differences (fewer in African American than in Caucasian people and more in East Asian people). The diagnosis of LOH is typically made using subjective symptoms and the serum testosterone concentration. The Aging Male Symptoms scale is widely used to evaluate the symptoms. The normal range of total testosterone concentration varies around the world; therefore, clinicians should follow the guidelines of their regional academic society. The principal treatment for LOH is TRT. There are many types of TRT and other treatment strategies are also available. Thus, physicians should treat LOH according to each patient's situation, considering related disorders, such as diabetes, osteoporosis, metabolic syndrome, and depression.