Creutzfeldt-Jakob disease: blood infectivity and screening tests.

Blood infectivity data from rodent models of transmissible spongiform encephalopathies (TSEs), and infectivity-prion protein (PrP) equivalence data from scrapie-infected hamster brain suggest a minimum requirement for PrP detection in blood buffy coat of < or = 10 pg/mL. This estimate could either be more or less stringent than calculated-more, if infectivity levels in human blood are lower than in experimental rodent models; less, if the infectivity-PrP ratio is lower in blood than in brain tissue, or if there is a large as yet undetected pool of abnormal but proteinase-sensitive PrP. None of several testing methods under development has yet achieved the calculated sensitivity requirement, but a few are within range, and it should be possible within the coming year to determine whether PrP occurs at a practically detectable level in the blood of patients with TSE.