The prostate-specific antigen (PSA) test is used as a way to identify the possible presence of prostate cancer. The prostate produces PSA, and the levels become elevated if there is cancer present or if some other prostate condition is present, such as inflammation (prostatitis). Normal prostate levels by age generally start with lower than 2.5 nanograms per milliliter under age 50 and go up from there.

If the prostate otherwise seems to be normal, a PSA level over 4 ng/mL is typically cause for at least some concern, up to a 15% chance of having prostate cancer. From 4 to 10, the chance is 25%. And over 10 the chance of having prostate cancer is 70%. In younger men, under age 50, anything about 2.5 ng/mL might be worth having investigated.

Keep in mind, however, that elevated PSA levels can be caused by any of the three main prostate diseases: cancer, enlarged prostate (BPH), and inflammed prostate (prostatitis). There is a high chance of false positives on any PSA test.

PSA levels generally increase with age as well. They tend to be around 4 for those aged 60, and around 7 for those aged 80. This is partially due to the tendency of the prostate to enlarge as men age, which can also raise PSA levels.

A PSA test is a useful tool for the diagnosis of possible problems, but since normal PSA levels by age generally increase, it is less than perfect and can indicate a host of problems with the prostate.