Almost all patients with prostate disease have heard of PSA testing, but they know almost nothing about PSA itself. So, what exactly is PSA? The Chinese name for PSA is “prostate-specific antigen”, which is a glycoprotein secreted by the prostate gland. This glycoprotein is very important for normal male reproductive function. First of all, PSA can liquefy the semen and facilitate the free movement of sperm in the semen. If PSA is below normal levels, it will lead to impaired liquefaction of semen, making men less fertile due to reduced sperm activity. Secondly, PSA also helps to dissolve uterine mucus, allowing sperm to enter the uterus smoothly. Abnormal PSA levels are likely to lead to male infertility. Interestingly, the initial discovery of PSA was closely associated with forensic medicine. Before the 1970s, PSA was discovered in male semen by researchers to assist in rape investigations, and with the help of PSA testing, traces of semen left behind by criminals could be found. Even now, PSA testing is still used by forensic doctors in such cases.