There is no clear cutoff for the normal range of the prostate specific antigen in men, reports Harvard Health Publications. Most United States doctors consider 4.0 nanograms per milliliter as normal, but since the levels increase with age, some suggest 2.5 nanograms per milliliter for men ages 40 to 49.
Many factors affect the results of a PSA test. If a man ejaculates or has a digital rectal exam before taking the blood sample, the levels increase temporarily. Medications, including statins or nonsteroidal anti-inflammatory drugs, cause levels to drop temporarily. While the evidence seems to show that screening does little to reduce the chances of death from prostate cancer, the decision for testing should remain between a man and his doctor, according to Harvard Health Publications.