The Prostate-Specific Antigen (PSA) serum test measures the level of PSA, a protein produced by the prostate gland, in the blood. Elevated PSA levels may indicate prostate enlargement, inflammation, or prostate cancer. The test is primarily used to screen for prostate cancer and to monitor the effectiveness of treatment in diagnosed patients. A blood sample is analyzed to detect abnormalities, with high levels prompting further diagnostic evaluation.