FWIW
PSA blood test was originally about 60/70% reliable, however they found that abstaining from sex for 24 hours prior improves the figure to 85%.

There is a better test (alleged by patentees) that compares the ratio of the two types of antigen (they claim). reliability of 95% is claimed. I am not sure how commonly available this test is. Reported in New Scientist 1 - 2 years ago.

The PSA test is not at it's best used on it's own. It is an indicator.