Sociodemographic and clinical characteristics of participants in blood p-tau217 studies for Alzheimer's disease: A systematic review.

Blood phosphorylated tau at threonine 217 (p-tau217) has shown considerable potential for the diagnosis of Alzheimer's disease (AD). For successful implementation in clinical practice, its applicability must be established across representative populations and settings. In this systematic review, we aimed to characterize participants included in p-tau217 research in AD, focusing on study setting, and sociodemographic and clinical features relevant to biomarker interpretation, and to assess how consistently these factors were reported across studies. A systematic review was conducted according to PRISMA guidelines. Observational studies assessing blood p-tau217 in the context of AD research were included. Data on study location, setting, and participant characteristics, including sociodemographic and medical conditions, were extracted. Across the 128 included studies, most participants were recruited from research cohorts (64.1%), primarily in North America (50.0%) and Europe (48.4%). Reporting of sociodemographic and clinical characteristics varied substantially, with several key variables available in only a minority of studies. Cognitively unimpaired participants represented the largest group (44.6%), and most participants were White (77.4%). By contrast, non-White populations, the oldest old, individuals with lower educational attainment, and those with greater clinical complexity were largely underrepresented. Overall, current evidence on p-tau217 is derived mainly from selected populations and may not fully reflect real-world clinical diversity. Differences in representation and in the reporting of clinically relevant factors may affect the biomarker's generalizability and interpretation. Future studies should prioritize more representative cohorts, and standardized reporting of key variables will be essential to strengthen its adoption in clinical practice.