MAPT and multiple system atrophy: p-tau181 differentiating: 1. Across cohorts AD vs. CU: AuROCs = 0.90–0.98 2. Validation cohort 1 AD vs. FTD: AuROCs = 0.76–0.82 with clinical diagnosis as reference ● Across cohorts tau-PET + vs. tau-PET-: AuROCs = 0.83–0.93 with tau-PET as reference; AD vs. Aβ-: AuROC = 0.99 with amyloid-PET as reference ● Validation cohort 2 - AD vs. VD: AuROC = 0.92 - AD vs. PSP/CBS: AuROC = 0.89 - AD vs. PD/MSA: AuROC = 0.82 with clinical diagnosis as reference ● Primary care cohort - AD vs. CU young adults: AuROC = 1.0 - AD vs. CU older adults: AuROC = 0.84 with clinical diagnosis as reference