The world population is aging. In China, with an increasing elderly population, the health problems that affect this group are becoming important public health concerns. With aging, a significant percentage of men develop a gradual and moderate decrease in testicular function known as late-onset hypogonadism (LOH), which is defined as "a clinical and biochemical syndrome associated with advancing age and characterized by typical symptoms and a deficiency in testosterone levels. It may result in significant detriment in the quality-of-life and adversely affect the function of multiple organ systems." [1],[2],[3],[4] As this definition implies, it is important to recognize and treat LOH appropriately if there are no contraindications. However, it was estimated that only 5%-35% of men experiencing LOH actually receive treatment for their condition [2] primarily because many LOH symptoms are similar to other conditions or are physiologically associated with the aging process. [2] No pathognomonic findings exist regarding specific androgen concentrations for clinically relevant subsets of older men. [2],[3],[4],[5] Therefore, the designation of a reliable testosterone threshold in aging males (below which hypogonadism-related symptoms emerge and adverse health outcomes ensue) is needed. Then, the use of arbitrary thresholds can be avoided. [3]

Recently, progress has been made in the study of male LOH. In an effort to define a syndrome of LOH, rather than a checklist of various symptoms, Wu et al. [3] reported the results of the European male aging study (EMAS) and concluded that the presence of three sexual symptoms (poor morning erection, erectile dysfunction, or low sexual desire) and a morning total testosterone level <11 nmol l−1 can be considered as evidence-based criteria for the diagnosis of LOH. However, as with the EMAS, most of the data regarding the advantages of diagnostic criteria for LOH have primarily been obtained from studies on Western populations. Therefore, studies to determine better criteria for Asian men, who may have different serum testosterone levels than Western men, are needed. Iwamoto et al. [6] reviewed the diagnostic criteria for LOH from several Asian countries and reported that the diagnostic methods for LOH in the International Society of Andrology (ISA), the International Society for the Study of Aging Male (ISSAM), and the European Association of Urology (EAU) recommendations are not necessarily feasible for men in Asian countries.

In a previous study, [7] we investigated LOH in elderly community-dwelling Chinese men using symptom score evaluation systems and measurements of sex hormone levels. However, no essential criteria for the LOH syndrome have been defined. With an improved analysis strategy, we reanalyzed the data to characterize the clinical symptoms associated with low testosterone levels and identified the essential criteria for LOH syndrome based on the presence of symptoms associated with low testosterone levels.

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