The Free PSA / Total PSA Ratio test is a blood test used to assess the risk of prostate cancer in men. PSA (Prostate-Specific Antigen) is a protein produced by the prostate gland. PSA exists in two forms: free PSA and bound PSA. The Free PSA / Total PSA Ratio compares the amount of free PSA to the total amount of PSA in the blood. This test is often used when the total PSA level is in a gray area where diagnosing prostate cancer is challenging. A low Free PSA / Total PSA Ratio may indicate a higher risk of prostate cancer. However, this test is not used to diagnose prostate cancer, but rather as a tool to help doctors assess risk and decide on next steps, such as a prostate biopsy.