Prostate Specific Antigen (PSA) is a protein produced primarily by cells in the prostate, a small gland that encircles the urethra in males and produces a fluid that makes up part of semen. Most of the PSA that the prostate produces is released into this fluid, but small amounts of it are also released into the bloodstream. PSA exists in two forms in the blood: free (not bound) and complexed (bound to a protein).

This test measures the amount of prostate specific antigen (PSA) in the blood. It was developed as a tumor marker to screen for and to monitor prostate cancer. It is a good tool, but not a perfect one. Elevated levels of PSA are associated with prostate cancer, but they may also be seen with prostatitis (inflammation of the prostate) and benign prostatic hyperplasia (BPH). Mild to moderately increased concentrations of PSA may be seen in those of African American heritage, and levels tend to increase in all men as they age.

PSA is not diagnostic of cancer. The gold standard for identifying prostate cancer is still the prostate biopsy, collecting small samples of prostate tissue and identifying abnormal cells under the microscope. The total PSA test and digital rectal exam (DRE) are used together to help determine the need for a prostate biopsy. The goal of testing is to minimize unnecessary biopsies and to detect clinically significant prostate cancer while it is still confined to the prostate.