Free PSA levels are not typically ordered as a stand-alone test. When evaluated alongside total PSA, free-PSA levels are a fairly accurate indicator of prostate cancer, according to Harvard Medical School.
Total PSA readings alone are not sufficient indication that further investigation is necessary, according to the National Cancer Institute. However, men who have a total PSA reading between 4 nanograms per milliliter and 10 nanograms per milliliter should have their free-PSA levels drawn, states Harvard Medical School. If the free-PSA levels are at 10 percent or less, there is a 56 percent chance that cancer is present. The most aggressive cancers are typically associated with the lowest free-PSA levels.