A prostate-specific antigen (PSA) test is a blood test that measures the level of PSA in a sample of your blood. PSA is a protein made by your prostate. The prostate is a gland in the male reproductive system. It lies just below the bladder. It makes the fluid part of semen.

A PSA test is used to screen for prostate cancer. Cancer screening means looking for signs of cancer before it causes symptoms. But screening tests can't diagnose cancer. If a screening test finds signs of cancer, you'll need other tests to find out if you have cancer and how serious it may be.

Source: MedlinePlus, U.S. National Library of Medicine