PSA, a prostate-specific antigen, is synthesized in both normal and cancer-like epithelial cells of the prostate. Under normal conditions, PSA is produced by prostate epithelial cells that secrete it directly into the prostatic ductal system. The normal prostate duct system is surrounded by a blood-epithelial barrier that prevents PSA produced by the prostate epithelium from entering the bloodstream directly, thus maintaining a low concentration of PSA in the blood. The higher the malignancy of the cancer, the greater the damage to the normal prostate tissue and the higher the PSA in the serum. This is why it is elevated in prostate cancer and is also its most important early detection indicator. However, non-malignant lesions of the prostate can also lead to elevated serum PSA, such as inflammation of the prostate, prostate enlargement, and acute urinary retention. The PSA in the blood will gradually increase with age and increase in prostate volume, but generally between 4-10ng/ml for senior prostate enlargement patients like you. The PSA can be increased 1-fold after rectal examination, 4-fold after cystoscopy, and 53-57-fold after prostate puncture biopsy or transurethral resection of the prostate. The PSA can also be increased by ejaculation in the normal state. Therefore, PSA testing should only be performed one week after the anal examination and at least 6 weeks after prostate biopsy and puncture. One way to differentiate between benign and malignant PSA elevations is to test for free prostate-specific antigen. PSA can exist in the serum in both free and bound forms. free PSA is the portion of PSA that is free in the plasma that is not bound, denoted as fPSA; total serum PSA is denoted as tPSA. fPSA concentration is lower in patients with cancer than in patients with benign hyperplasia. It is this difference that is applied clinically to screen out early prostate cancer from patients with BPH by applying the fPSA/tPSA ratio. The reference value is 0.16, i.e., a ratio <0.16 is associated with a high probability of prostate cancer.