A false-positive PSA result can occur due to benign prostate enlargement, a prostate infection, or another condition not related to prostate cancer, explains Mayo Clinic. False-positive PSA test results are common and only one in four men with a positive result has prostate cancer.
PSA test results can also be false negative in patients with rapidly growing prostate cancer, according to Mayo Clinic. In this case the cancer grows too fast and does not produce a lot of PSA. In the past, doctors recommended a yearly routine PSA screening for prostate cancer for all men over the age of 50 and PSA levels above 4.0 nanograms per milliliter required a follow-up prostate biopsy. This is no longer indicated because studies have found that many patients with elevated PSA levels do not have prostate cancer and some men with low PSA levels do.
Recommendations for prostate cancer screening in 2015 include a thorough discussion between the patient and his doctor regarding the risks, benefits and doubts of screening before any testing takes place, suggests the American Cancer Society. Men who have an average risk for prostate cancer and a life expectancy of more than 10 years can begin this discussion at the age of 50 years.