Alzheimer’s disease involves multiple pathological processes that emerge and evolve across the disease continuum, creating a need for biomarkers that capture different aspects of disease biology. Plasma phosphorylated tau biomarkers, particularly pTau 217, have demonstrated strong associations with amyloid pathology, however no single biomarker captures the full complexity of disease biology. This webinar explores how ultrasensitive protein detection enables the measurement of plasma eMTBR-Tau, an emerging blood-based biomarker associated with tau tangle pathology in Alzheimer’s disease. Additional biomarkers are needed to investigate the accumulation of insoluble tau aggregates and neurofibrillary tangles, which are more closely associated with disease stage and cognitive decline. The endogenous microtubule-binding region of tau, or eMTBR-Tau, is enriched in the filament cores that form neurofibrillary tangles. Emerging evidence indicates that specific MTBR-Tau fragments in biofluids may offer a blood-based window into tau aggregate pathology. Measuring these extremely low-abundance species in plasma, however, requires highly sensitive and specific analytical methods. The webinar will provide an overview of an ultrasensitive, homogeneous, wash-free immunoassay approach and explain how standard qPCR readout support measurement of low-abundance protein biomarkers from 1 µL sample volumes. The featured speaker will also discuss the evolving landscape of blood-based tau biomarkers and explain how eMTBR-Tau offers distinct biological insights from established phosphorylated tau markers. The panelist will examine the potential role of plasma eMTBR-Tau in studying the transition from early amyloid-associated tau changes to more advanced tau tangle pathology. The speaker will review results from amyloid- and tau-PET–characterized research cohorts. They will also discuss potential