PSA is a blood test that has been available for over 20 years. Prior to its discovery only rectal exams where done to discover the possibility of prostate cancer.
PSA is a protein produced only in the prostate and measured by a blood test. It does increase slowly with age. It has proven to be a very valuable test in early detection of prostate cancer. Since PSA was discovered prostate cancer deaths have decreased by over 20%.
PSA is a big help in early detection of prostate cancer. But not all abnormal PSA means cancer; it only means further investigation may be warranted. These tests may include Prostate Ultrasound and Biopsy.
In any cancer early diagnosis leads to a better chance of a cure.
There is controversy on the benefits of PSA testing because of the expense involved in prostate biopsy , prostate surgery, radiation and any associated complications. All these need to be discussed with your urologist, or read more on Mayo Clinic