A "Negative" result has the following standard definition. Based on current transmissible spongiform encephalopathy (TSE) research and pathogenesis studies, it is possible to have protease resistant prion protein present at levels below the sensitivity of this test. It should also be noted that protease resistant prion protein may be present in tissues other than those that were examined. This analysis was performed and validated using scrapie positive brain or lymph node tissues as controls.