PSA is an acronym for a protein called prostate specific antigen. For many males as they age, the prostrate enlarges and restricts the urethra, a malady known as BPH (benign prostate hypertrophy). This is the cause of frequent urination, inability to empty the bladder and a constant feeling of the need to urinate in old guys. At home, these symptoms are merely annoying; in a tent on a rainy night the symptoms are beyond annoying and are one reason for a lot of older male backpackers carrying a bottle in which to pee at night.

A man's PSA level will increase gradually as the prostate enlarges with age but will normally not exceed 3-4. The PSA level in a young male is generally 2 or less. A sudden increase in PSA or values above age-normal can indicate the presence of a tumor. A good physician will always do both a PSA screen and a digital exam. If any suspicion arises from these procedures, then a needle biopsy is ordered to evaluate the biopsy material for prostate cancer.