Free prostate specific antigen

Prostate specific antigen (PSA) is a single-chain glycoprotein secreted by prostate gland. It exists in epithelial cells of prostate duct and has prostate tissue specificity. about 10%-20% of serum PSA exists in free form, called free PSA, and the rest exists in bound form. The sum of the two is called total PSA. Therefore, clinical prostate tumor marker examination can be generally divided into three items: Total PSA, free PSA, and ratio of the two. Free PSA alone has little diagnostic significance for prostate cancer, but when serum total PSA is between 4 and 10 ng/ml, free PSA levels are negatively correlated with prostate cancer incidence. Free prostate specific antigen is an effective method to increase the detection rate of prostate cancer in gray areas with total prostate specific antigen levels. When serum total prostate specific antigen is between 4 and 10 ng/ml, abnormal free prostate specific antigen to total prostate specific antigen ratios require prostate biopsy.