Antigen is a form of protein produced by the cells of the prostate gland. When a man has a prostate-specific antigen blood test (PSA) done, the test measures the level of PSA in the blood. PSA is produced by the body, thus testing it is an accurate and reliable way to check for tumors and cancers. Age has a significant impact on the levels of PSA in the blood and a variation in the levels could also be a red flag for prostatitis (an inflamed prostate) and benign prostatic hyperplasia (an enlarged prostate). The PSA test alone cannot fully diagnose whether or not cancer is present, however, performing the test along with a digital rectal exam can detect cancer in men 50 years of age and older.