Prostate specific antigen (PSA) is a protein that is made in the prostate in two forms – complexed and free. Complexed PSA is bound to other proteins, while free PSA is not bound to anything. Total PSA tests are mainly used to screen for prostate cancer; however, it is not specific enough to diagnose prostate cancer on its own. Free PSA tests can help men with slightly high total PSA levels to help determine whether or not they should get a prostate biopsy. Prostate tumors normally produce complexed PSA, while normal prostate cells produce free PSA. Free PSA tests are used to find the PSA free/total ratio. A high ratio means that you do not need a prostate biopsy.