PSA is a protein produced mainly by cells in the prostate gland and can be a useful indicator of prostate cancer. This protein can be found in all males; however, men whose levels are increased may have an infection of the prostate gland (prostatitis), prostate enlargement or prostate cancer. In blood, PSA is present both as free PSA and as complexed PSA bound to other blood proteins. The free PSA test measures the percentage of the total PSA that is not bound to proteins in the patient’s blood.