Plasma p‐tau217 detects Alzheimer's disease co‐pathology in cerebral amyloid angiopathy: Comparison to CSF biomarkers in the ANGMAR cohort

INTRODUCTION: Cerebral amyloid angiopathy (CAA) frequently co-occurs with Alzheimer's disease (AD), generating mixed vascular-neurodegenerative phenotypes. Plasma phosphorylated tau (p-tau)217 is a robust biomarker of AD, but its performance in CAA remains unclear. METHODS: We studied 231 participants, including 50 patients with CAA (Boston v2.0), 154 with AD, and 27 cognitively unimpaired controls. Plasma p-tau217 was measured on an automated platform and compared to cerebrospinal fluid (CSF)-defined AD status. Associations with magnetic resonance imaging (MRI) markers of CAA burden were evaluated. RESULTS: Among CAA participants, 29 met CSF criteria for AD co-pathology. Plasma p-tau217 discriminated CAA patients with and without AD co-pathology (area under the curve = 0.920) and showed no association with MRI markers of CAA burden. Predefined cut-offs (≥ 0.27 pg/mL and ≥ 0.34 pg/mL) yielded high accuracy for identifying AD co-pathology within CAA. CONCLUSIONS: Plasma p-tau217 shows high diagnostic accuracy for identifying AD co-pathology in CAA and is not associated with MRI markers of CAA burden, supporting its specificity for AD-related pathology.