A Two-Stage Plasma Biomarker Algorithm Reduces Amyloid PET Use and the p-Tau217 Gray Zone

Objective

Plasma p-Tau217 leaves 30%-50% of patients in an indeterminate "gray zone" often requiring Aβ-PET. We developed GRAD (Gatekeeper-Reflex for Alzheimer's Disease), a two-stage Aβ-positivity prediction model to improve classification while reserving Aβ-PET for residual uncertainty.