CSF biomarkers and plasma p‐tau181 as predictors of longitudinal tau accumulation: Implications for clinical trial design

Introduction Clinical trials targeting tau in Alzheimer's disease (AD) need to recruit individuals at risk of tau accumulation. Here, we studied cerebrospinal fluid (CSF) biomarkers and plasma phosphorylated tau (p‐tau)181 as predictors of tau accumulation on positron emission tomography (PET) to evaluate implications for trial designs. Methods We included older individuals who had serial tau‐PET scans, baseline amyloid beta (Aβ)‐PET, and baseline CSF biomarkers (n = 163) or plasma p‐tau181 (n = 74). We studied fluid biomarker associations with tau accumulation and estimated trial sample sizes and screening failure reductions by implementing these markers into participant selection for trials. Results P‐tau181 in CSF and plasma predicted tau accumulation (r > 0.36, P 0.37, P