MAPT and tauopathy: Immunoprecipitation–MS assays developed for other such fluid-based biomarkers (Aβ42/40, tau, phospho-tau, tau-MTBR) have shown advantages of high analytical precision, improved sensitivity and specificity of determining disease state and distinguishing tauopathies.22-27 Here, we present a novel method for IP and quantitation of NfL in blood by MS.