PSA, also known as prostate-specific antigen, is a single-chain glycoprotein found in the epithelial cells of the prostate ducts. tPSA, which can also be called serum total prostate-specific antigen, can contain t-PSA as well as f-PSA, and t-PSA, which can be called serum total PSA, exists in serum in both a bound and a free form, where the free form can be called f-PSA. When t-PSA and f-PSA are elevated, but the f-PSA/t-PSA ratio is lowered, then it represents prostate cancer. t-PSA＜4.0μg/L, f-PSA＜0.8μg/L, f-PSA/t-PSA ratio＞0.25 is normal, if it is higher or lower than that, then it is necessary to improve the other tests to make a clear diagnosis.