Xiao Zhang is a young guy, but he could not make his wife pregnant due to his little sperm production, which made him deeply distressed. After coming to the clinic, the doctor prescribed him a sex hormone test. Zhang was puzzled: What does sperm production have to do with the substances in the blood? What exactly is the intrinsic connection between sex hormones and fertility? Introduction of sex hormones Common sex hormone tests include FSH, LH, T, PRL and E2, which represent follicle stimulating hormone, luteinizing hormone, testosterone, pituitary lactogen and estradiol respectively. The specific meanings and significance are as follows: 1. Serum follicle stimulating hormone (FSH) and luteinizing hormone (LH) The synthesis and secretion of serum follicle stimulating hormone (FSH) and luteinizing hormone (LH) are mainly regulated by gonadotropin releasing hormone (GnRH), which promotes the secretion of FSH and LH. These two hormones are regulated not only by GnRH but also by negative feedback from testosterone (T) and estradiol (E-2). They act like a hub for these hormones and are a very important endocrine hormone. In men, FSH acts mainly on the spermatogenic and supporting cells of the testes, and LH acts mainly on the interstitial cells of the testes. When men have problems with spermatogenesis, the feedback regulation of hormones will make the levels of FSH and LH abnormal. These two indicators can not only reflect whether the spermatogenic function is normal, but also further classify the spermatogenic abnormalities, which plays a very important role in the follow-up treatment of clinicians. 2.Serum testosterone (T) Testosterone (T) is mainly secreted by the interstitial cells of the testes, also known as “androgens”. Only about 2% of testosterone in plasma exists in free form, and the testosterone in this form is biologically active, while the majority of the rest is bound to plasma proteins. Testosterone has very important physiological roles, such as inducing the differentiation of Y chromosome-containing embryos into males, promoting the development of internal genitalia; maintaining spermatogenesis; stimulating the growth of accessory organs and maintaining libido; also promoting the synthesis of proteins especially in muscles and reproductive organs and the growth of bones. When the testicular function is abnormal, it may affect the secretion of T. This will make the libido decrease, slow down the growth of sexual organs, and decrease the sperm production, etc. 3.Serum pituitary lactogen (PRL) Pituitary lactogen (PRL) is a protein hormone secreted by the pituitary gland, which can indirectly reflect the function of the pituitary gland. The pituitary gland is the hub of the “hypothalamic-pituitary-target organ” axis, and when there are problems with it, PRL may be abnormal, as well as other sex hormones, It is also likely to be influenced by the external environment: when there are mood swings, stress, or increased pressure, PRL may rise non-pathologically. Estradiol (E2), often referred to as “estrogen”, promotes and regulates the normal development of female sexual organs and paraphilias. In normal men, there is also a small amount of estrogen in the body, because the testicular interstitial cells can secrete a small amount of estrogen. However, when a large amount of estrogen is present in a man, it may be due to a decrease in androgen production and it suggests abnormalities in the function of the testes. Why are these tests done? Sex hormone tests are a very important part of the male examination. Their increase or decrease has a very important clinical significance, not only reflecting the normal function of the organ, but also playing a very important role in the diagnosis of different types of male infertility. For example, when the basal levels of LH and FSH are significantly increased, it indicates testicular failure; when the basal levels of FSH and LH are reduced or at the low limit of normal, the lesion may be in the hypothalamus or pituitary gland, which is secondary to hypogonadotrophic hypogonadism (HH). Then again, a markedly elevated PRL level with low or normal low limit FSH and LH with hypogonadism, oligospermia, ED (erectile dysfunction), etc. may be hyperprolactinemia or lactinoma or pituitary microadenoma. If the PRL level is >200ug/L, the presence of a pituitary tumor is almost certain. T values also have very important clinical significance when analyzed in combination with other hormones. For example, when FSH and LH are elevated, a decrease in T or T/LH ratio is typical of hypergonadotropic hypogonadism, suggesting primary testicular failure, such as Crohn’s syndrome, severe varicocele, etc. A decrease in T level or an increase in E2 level with a decrease in T/E2 ratio can be seen in various causes of testicular hypogonadism.