According to WebMD, PSA stands for prostate-specific antigen, a substance produced by the prostate gland. High levels suggest a risk of prostate cancer, and levels between 2.5 and 4 nanograms per milliliter of blood are usually considered normal.
WebMD further mentions that normal levels of PSA depend on the age of the patient, and levels higher than 2.5 may be of concern to younger patients. Men with PSA levels between 4 and 10 are considered to have a 25 percent risk of developing cancer. For a complete risk assessment, PSA tests are coupled with a physical examination of the prostate.