Free prostate-specific antigen is a reference indicator initially used to screen for prostate cancer, and the normal reference value given is 0-1ng/ml. Therefore, it is normal for free prostate-specific antigen to be low, and in normal people free prostate-specific antigen can be as low as 0, that is, to the extent that it is undetectable. However, the results obtained from the analysis of the free prostate-specific antigen index alone are not clinically significant. If the total prostate-specific antigen is less than 4 ng/ml, the possibility of prostate cancer can be excluded. The smaller the ratio is, the greater the risk of prostate cancer, and a ratio greater than 0.16 is less likely to be malignant.