Prostate-specific antigen (PSA) is a protein produced by the cells of the prostate gland, which is located below the bladder in men. PSA is primarily found in semen, but small amounts can also be detected in the blood. It plays a role in liquefying semen, helping sperm to swim more freely. Doctors often measure PSA levels through a blood test to screen for prostate cancer or other prostate-related conditions. Elevated PSA levels may indicate the presence of cancer, but they can also result from benign conditions like prostatitis or benign prostatic hyperplasia (BPH).