Prostate-specific antigen (PSA), also known as gamma-seminal plasma or kinin-releasing enzyme 3 (KLK3), is a glycoprotein that in humans is encoded by the KLK3 gene.PSA is a member of the kinin-releasing enzyme-related family of peptidases, and is produced by secretion from the epithelial cells of the prostate gland. Ejaculation produces PSA, which liquefies semen clots and allows sperm to swim freely.PSA also dissolves cervical mucus, allowing sperm to enter the uterus. Men with normal prostate glands have only a small amount of PSA in their serum, whereas patients with prostate cancer or other prostate dysfunction tend to have elevated levels of PSA in their serum. Obesity has been reported to decrease serum PSA levels. Prostatitis, irritation, and benign prostatic hyperplasia increase PSA levels and produce false-positive results.PSA is not the only indicator for diagnosing prostate cancer, but can also detect prostatitis or benign prostatic hyperplasia. Thirty percent of patients with high levels of PSA are diagnosed with prostate cancer after biopsy. Clinical practice guidelines for prostate cancer screening vary and are controversial because it is uncertain whether the benefits of screening outweigh the risks of overdiagnosis and overtreatment.