Prostate-specific antigen (PSA) is a single-chain glycoprotein with serine protease activity synthesized primarily by prostate epithelial cells and present in large amounts in semen, which breaks down the major colloidal proteins in semen, participates in the liquefaction process of semen, and is associated with male fertility. A barrier exists around the normal prostatic ductal system that prevents PSA produced by the prostatic epithelium from entering the bloodstream directly, thus maintaining a low concentration of PSA in the blood. PSA in the blood is the sum of free PSA (fPSA) and complex PSA, also known as total PSA (tPSA), which is tissue-specific and is only synthesized by prostate epithelial cells and is not expressed in other cells. However, it is not tumor specific. Prostatitis, benign prostatic hyperplasia and prostate cancer can all result in total PSA levels. Serum total PSA is affected by age, race, prostate size and other factors. The normal range of serum total PSA in our population is lower than in the population of western countries; the younger the age and the smaller the prostate, the lower the normal range of serum total PSA. In addition, rectal examinations, indwelling catheterization, and acute prostatitis can all lead to an increase in serum total PSA. Therefore PSA test should be performed 24 hours after ejaculation, 48 hours after cystoscopy, catheterization and other operations, 1 week after rectal examination of the prostate, 1 month after prostate puncture and exclude diseases such as acute prostatitis. The current consensus at home and abroad is that a total serum PSA of less than 4.0 ng/ml is normal, and a total serum PSA of more than 10 ng/ml increases the risk of anterior adenocarcinoma. When cancer occurs in the prostate gland, the barrier of the prostate ducts will be destroyed and the PSA secreted by the cancer will increase, resulting in PSA entering the bloodstream directly. The more malignant the cancer is, the more damage it does to normal prostate tissue, and the higher the serum PSA. At a total serum PSA of 4-10 ng/ml, it is difficult to distinguish between prostate enlargement and prostate cancer based solely on the total serum PSA level. In this so-called gray area, reference to parameters such as free prostate-specific antigen (fPSA), PSA density (PSAD) and PSA rate (PSAV) are recommended. A total serum PSA greater than 4.0 ng/ml is considered abnormal. If it is abnormal, interfering factors should be ruled out first, and if you are unsure, you can retest again in 4 weeks. After rechecking, if serum tPSA4~10 ng/ml, f/t PSA is abnormal (<0.16< span="">) or PSAD value is abnormal (>0.15), a prostate puncture biopsy is required. If the serum tPSA is 4~10 ng/ml, if the f/t PSA, PSAD values and imaging are normal, close follow-up should be performed. If the serum tPSA is >10 ng/ml, a prostate puncture biopsy is required.