Alzheimer's Disease clinical decision points for two plasma p-tau217 laboratory developed tests in neuropathology confirmed samples

INTRODUCTION: We evaluated the diagnostic performance of two commercial plasma p-tau217 immunoassays compared to CSF testing and neuropathology. METHODS: 170 plasma samples from University of British Columbia Hospital Clinic for Alzheimer's (AD) and Related Disorders were analyzed for p-tau217 using Fujirebio and ALZpath assays. Decision points were determined using CSF testing and autopsy findings as the standard. RESULTS: Fujirebio and ALZpath p-tau217 had similar overall analytical and clinical performance, with distinct decision points for each assay. Based on autopsy finding, both p-tau217 assays identified individuals with AD from other neurodegenerative diseases (ALZpath AUC = 0.94, Fujirebio AUC= 0.90). The ALZpath assay detected AD pathology at milder disease stages compared to the Fujirebio assay. DISCUSSION: Our study reinforces the clinical utility of plasma p-tau217 as an AD biomarker. Differences in test performance and clinical decision points suggest an assay specific diagnostic approach is required for plasma p-tau217 in clinical practice.