Patients usually do not need to fast before having a prostate-specific antigen blood test, according to MedlinePlus. It is important for patients to inform their doctors of their current medications, as certain medicines may falsely lower the PSA level.
A PSA test may be performed as a screening tool for prostate cancer or to determine if prostate cancer has returned after treatment is finished, explains MedlinePlus. Doctors may also order a PSA test if a patient's prostate exam is abnormal. Several conditions lead to elevated PSA levels, including enlarged prostates, prostatitis, prostate cancer and urinary tract infections. When determining the significance of an elevated PSA level, a doctor considers factors such as the patient's age, risk factors and PSA level history.