Diagnostic value of plasma phosphorylated tau181 in Alzheimer’s disease and frontotemporal lobar degeneration

With the potential development of new disease-modifying Alzheimer’s Disease (AD) therapies, simple, widely available screening tests are needed to identify which individuals who are experiencing symptoms of cognitive or behavioral decline should be further evaluated for initiation of treatment. A blood-based test for AD would be a less invasive and less expensive screening tool than the currently approved CSF or amyloid β-PET diagnostic tests. We examined whether plasma phosphorylated tau at residue 181 (pTau181) could differentiate between clinically diagnosed or autopsy confirmed AD and Frontotemporal Lobar Degeneration (FTLD). Plasma pTau181 concentrations were increased by 3.5 fold in AD compared to controls and differentiated AD from both clinically diagnosed (Receiver Operating Characteristic Area Under the Curve [AUC]=0.894) and autopsy confirmed FTLD (AUC=0.878). Plasma pTau181 identified amyloid β-PET positive individuals regardless of clinical diagnosis and correlated with cortical tau protein deposition measured by (18)F-Flortaucipir PET. Plasma pTau181 may be useful to screen for tau pathology associated with AD.