Diagnostic performance of plasma p-tau217 and Aβ42/40 biomarkers in the outpatient memory clinic

Abstract

INTRODUCTION: Plasma biomarkers of Alzheimer's disease (AD) represent accessible alternatives to positron emission tomography (PET) and cerebrospinal fluid (CSF)-based biomarkers in well-characterized cohorts. It remains to be determined whether performance is maintained in outpatient clinics comprised of patients with multiple causes of cognitive impairment. METHODS: Plasma phosphorylated tau217 (p-tau217) and amyloid beta (Aβ) 42/40 were measured in 509 patients evaluated in a tertiary-care memory clinic. Biomarker performance was compared across diagnoses, referencing established cutpoints for positive and negative biomarkers. RESULTS: Plasma p-tau217 distinguished patients with diagnoses of symptomatic AD with 95% sensitivity and 82% specificity. Integration of Aβ42 measurements (p-tau217/Aβ42) incrementally improved specificity (86%). Plasma p-tau217 and p-tau217/Aβ42 concentrations closely associated with established CSF biomarkers of AD (area under the curve [AUC]: 0.94 and 0.96, respectively). Reduced kidney function associated with elevated plasma p-tau217 and p-tau217/Aβ42 concentrations in patients without AD (referencing CSF biomarkers). DISCUSSION: Plasma p-tau217 and p-tau217/Aβ42 concentrations demonstrated robust diagnostic performance in a heterogeneous clinical cohort; interpretation requires consideration of kidney function. Highlights: Plasma phosphorylated tau217 (p-tau217) reliably identified clinic patients with Alzheimer's disease. A two-cutpoint strategy yielded definitive results in 86% of patients. Integration of plasma amyloid beta (Aβ; p-tau217/Aβ42) minimally improved diagnostic performance. Plasma p-tau217 levels were increased in patients with kidney dysfunction.