Prostate-specific antigen (PSA) can be categorized into two types: total PSA, which has a normal value of 0-4 ng/mL, and free PSA, which has no normal value. Prostate-specific antigen is a glycoprotein produced by plasma vesicles in the epithelial cells of the normal or cancerous prostate, and the more severe the disease, the higher its value. In general, two indicators can be used to screen the prostate for tumors. First of all, you need to take a blood test, if the value of total psa is below 4ng/ml, and if there is no problem in combination with the imaging examination, there is usually no prostate tumor. However, if the total psa value is above 10ng/mL, it is recommended that the patient, regardless of the imaging results, undergoes a prostate aspiration biopsy to investigate whether he has a prostate tumor. This is because a psa value of more than 10 ng/mL is associated with a 50% probability of having a prostate tumor. If the total psa value is between 4-10ng/ml, we should refer to the free psa value. Generally, we should refer to the ratio of the total psa value to the free psa value, which is around 0.16 is the normal limit. If the ratio is below 0.1, the probability of having prostate tumor is more than 50%. If the ratio is above 0.25, the probability that the patient is a prostate cancer is just below 10%.