PSA (prostate specific antigen) blood serum is a non-invasive preventive blood test used to detect prostate cancer in men. PSA is produced by normal, abnormal and cancerous prostatic tissue. The PSA blood test is an accurate measure of this amount. The theory is that cancer causes more of the protein to be made and leaked into the blood than normal prostate tissue, so PSA is now used for assisting in the diagnosis and monitoring of prostatic carcinoma. More men are having regular serum PSA determinations, as part of an early detection program. There's no doubt that the use of PSA testing has resulted in an increase in the number of men having prostate biopsies and subsequently being diagnosed with cancer, with a shift towards detection at earlier stages.