A prostate-specific antigen (PSA) test measures the amount of prostate-specific antigen in the blood. PSA is released into a man's blood by his prostate gland. Healthy men have low amounts of PSA in the blood. The amount of PSA in the blood normally increases as a man's prostate enlarges with age. PSA may increase as a result of an injury, a digital rectal exam, sexual activity (ejaculation), inflammation of the prostate gland (prostatitis), or prostate cancer.
Prostate cancer often grows very slowly, without causing major problems. Detecting prostate cancer early and treating it may prevent some health problems and reduce the risk of dying from the cancer. However, some treatments for prostate cancer can cause other problems, such as controlling urination (incontinence) or erection problems (erectile dysfunction). Some men may choose not to have a PSA test or treat prostate cancer if it is detected. For example, a man older than age 75 who has no bothersome symptoms of prostate cancer may choose not to treat the cancer if it is found, so he would not need a PSA test.