Plasma Phosphorylated Tau 217 and Amyloid Burden in Older Adults Without Cognitive Impairment: A Meta-Analysis.

Importance: Blood-based biomarkers (BBMs) demonstrate high accuracy in detecting Alzheimer disease (AD) pathological changes in symptomatic individuals. In autosomal dominant AD and in individuals with Down syndrome, both populations with near-universal development of AD pathology, elevations in BBMs are detectable years before clinical onset, supporting their utility for identifying preclinical disease in these cases. Among BBMs, plasma phosphorylated tau 217 (p-tau217) exhibits strong concordance with established in vivo markers of AD pathology. However, its ability to identify older adults without cognitive impairment who are amyloid-positive remains variable across studies and settings. Objective: To assess the standardized effect size of mean differences and classification accuracy of p-tau217 for published studies that compared amyloid-positive and amyloid-negative older adults without cognitive impairment. Data Sources: PubMed, Embase, and EBSCOhost databases from inception to September 1, 2025. Study Selection: Observational studies or randomized clinical trials with baseline data on individuals without cognitive impairment who were classified as either amyloid positive or amyloid negative and reported numeric data for p-tau217 levels. Data Extraction and Synthesis: The Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) reporting guideline was used for this study. Two authors independently carried out literature searches to identify studies with older adults without cognitive impairment who were classified as either amyloid positive or amyloid negative where p-tau217 was quantified. Main Outcome and Measure: The standardized mean difference (Hedges g) was used to characterize differences in mean p-tau217 levels. A pooled area under the curve (AUC) value was used to summarize the diagnostic accuracy of p-tau217 in identifying amyloid-positive individuals. Between-study heterogeneity was investigated using subgroup and sensitivity analyses. Publication bias was assessed using Egger tests. Results: Data for 7834 participants (2533 amyloid positive, 5301 amyloid negative) from 18 publications were analyzed. A large effect size was observed for p-tau217 (Hedges g = 1.50; 95% CI, 1.33-1.68). Values for p-tau217 also demonstrated high accuracy for identifying amyloid-positive individuals without cognitive impairment (AUC = 0.87; 95% CI, 0.85-0.90). Conclusion and Relevance: These findings demonstrate that plasma p-tau217 can reliably detect AD pathology in the preclinical stage. These findings support the clinical utility of plasma p-tau217 as a scalable, minimally invasive tool for early identification of AD, particularly in settings where timely intervention with disease-modifying therapies may offer the greatest benefit in slowing or preventing disease progression.