This blood test measures prostate-specific antigen (PSA), a protein made by the prostate gland. It reports total PSA, free PSA (the portion not bound to blood proteins), and the percent free PSA (free PSA as a percentage of total PSA). The percentage is often used to help interpret results when total PSA is in a borderline range. The test is used to evaluate prostate health in individuals with a prostate. It may be ordered to help assess an elevated total PSA, monitor known prostate conditions, or provide additional information when deciding whether further evaluation is needed. The percent free PSA can help distinguish between benign prostate conditions and other causes of an elevated PSA.