Abnormal levels of PSA, or prostate-specific antigen, generally do not exist, states the National Cancer Institute. Historically, PSA levels above 4.0 nanograms per milliliter often required a prostate biopsy to test for cancer, but studies show that prostate cancer can exist in patients with PSA levels below this figure.
PSA levels above 4.0 are not necessarily indicative of prostate cancer, according to the National Cancer Institute. The unreliability of PSA testing is in part due to the fluctuation of PSA levels in a man, which can increase due to factors such as urinary tract infections, prostatitis, prostate biopsies and prostate surgery. Finasteride and dutasteride are medications that can lower PSA levels. Additionally, testing differences between laboratories can also display varied results.