pTau217 immunoassays in Alzheimer's disease continuum: A comparative study of Ella and Lumipulse

Background; Plasma phosphorylated tau 217 (pTau217) has emerged as one of the most accurate biomarkers for Alzheimer's disease (AD). However, direct comparisons of pTau217 levels between different automated immunoassays remain limited.ObjectiveIn this context, our work aimed to compare Lumipulse and Ella platforms for the measurement of plasma pTau217 across the AD continuum.MethodsBlood samples were collected from 32 subjective cognitive decline (SCD), 25 mild cognitive impairment (MCI), and 10 Alzheimer's disease (AD) patients. Plasma pTau217 levels were assessed using Lumipulse G600II automated system and Ella immunoassay SR-X platform. Associations with clinical variables and agreement between platforms were assessed.ResultsPlasma pTau217 levels increased from SCD to AD with both assays. Lumipulse showed a significant difference between SCD and AD (p = 0.0011), while Ella detected differences between SCD and MCI (p = 0.0198) and SCD and AD (p = 0.0001). Both assays showed a significant inverse correlation with Mini-Mental State Examination (Lumipulse: r = -0.4913; p = 0.0001. Ella: Pearson r = -0.5139; p = 0.0001). A moderate correlation between platforms was observed. Bland-Altman analysis revealed a negative bias, with Lumipulse yielding lower values than Ella and increasing variability at higher concentrations.ConclusionsLumipulse and Ella provided consistent qualitative information on plasma pTau217 across the AD continuum and show similar associations with cognitive performance, meaning that they are both comparable techniques. However, systematic bias and proportional variability limit their quantitative interchangeability, highlighting the need for cross-platform standardization.