Normal semen consists of two main components: sperm and seminal plasma. Seminal plasma consists of approximately 30% prostatic fluid, 65% seminal vesicle fluid and 5% urethral bulb gland fluid. The fructose secreted by the seminal vesicle glands is hidden in the seminal fluid. Spermatozoa are produced in the testes and are transported via the vas deferens to rendezvous with seminal plasma near the ejaculatory ducts after maturation. The significance of detecting seminal plasma fructose is twofold: (1) the physiological significance of fructose levels; and (2) fructose, as a secretory substance unique to the seminal vesicle gland, can reflect the function of the seminal vesicle gland or the discharge of seminal vesicle fluid, which can further indicate related diseases. Glucose in seminal fluid is the direct source of energy for spermatozoa. Although seminal plasma contains fructose, spermatozoa cannot use fructose directly for energy and need to process the fructose in semen into glucose before it can be ingested. Almost all of the glucose in semen is converted from fructose, which is the “behind-the-scenes” energy source for sperm. When the fructose content in the semen decreases, the amount of glucose processed into glucose will be reduced accordingly, and the sperm will be in a “starved” state due to insufficient energy supply, and will swim weakly or even be “starved to death”. Therefore, when the ejaculated semen contains spermatozoa and the fructose content in seminal plasma is low, there will be insufficient sperm supply and reduced motility. The level of testosterone affects the secretion of fructose in seminal vesicles, and androgen deficiency can cause a decrease in fructose content. In men, androgens tend to decline with age, and the secretion function of seminal vesicles decreases, with a consequent decrease in seminal plasma fructose content and a decrease in semen volume. Therefore, the continuous decrease of seminal plasma fructose concentration can also reflect the decrease of male androgen level to a certain extent. When the seminal vesicle gland is underdeveloped, fibrotic or infected, the secretion function of the seminal vesicle gland is reduced, and the fructose discharge into the semen is consequently reduced. The decrease in fructose secretion is often accompanied by a decrease in semen volume. In cases of incomplete obstruction of the seminal vesicle drainage ducts and ejaculatory ducts, the discharge of seminal fluid is obstructed, resulting in a decrease in seminal plasma fructose content and semen volume. In seminal vesiculitis, the amount of seminal plasma fructose is reduced and the semen is often light brown in color. If the seminal vesicle gland is congenitally deficient, no fructose is detected in the semen and the ejaculated semen shows no spermatozoa, low semen volume, and semen pH is usually less than 7. If the ejaculatory duct is obstructed, even if the seminal vesicle gland is normally developed, no fructose is detected in the ejaculated semen and the semen behaves as if the seminal vesicle gland is congenitally deficient. The above two conditions are collectively referred to as distal obstructive azoospermia, in which the transport duct of sperm is obstructed or interrupted to the extent that the sperm in the testes cannot be discharged.