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 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.