Analytical and clinical performance of eight Simoa

backgroundAmong the Alzheimer's disease (AD) biomarkers measured in blood, phosphorylated forms of tau (p-tau) have been shown to exhibit a particularly high diagnostic potential. Here, we performed a comprehensive method comparison study, followed by evaluation of the diagnostic performance of eight recent plasma p-tau immunoassays targeting different tau phosphorylation sites, different tau fragments, and that are measured by two distinct platforms.

methodsWe enrolled a cohort of 40 patients with AD at the stage of dementia (AD-dem) characterized by positive CSF A + T + profile, and a control group of 40 cognitively healthy participants (Control), to conduct a comprehensive method comparison for three plasma p-tau181 and five plasma p-tau217 assays run on the Simoa

resultsWe found a strong, positive correlation between all the measurements. Fixed and/or proportional bias was observed for each of compared p-tau181 assay pairs or p-tau217 assay pairs. While both plasma p-tau181 and p-tau217 levels were significantly increased in AD-dem vs. Control groups as measured by all assays, higher median concentration AD-dem/Control fold change and AUC values were observed for p-tau217 (assays range: fold change 3.72-6.74, AUC 0.916-0.956) compared with p-tau181 (assays range 1.81-2.94, AUC 0.829-0.909), independently of the platform used. No significant differences were observed between diagnostic performance of p-tau181 assays or p-tau217 assays targeting tau N-terminus or mid-region.

conclusionsAlthough all plasma p-tau measurements enabled discrimination between clinical groups, p-tau217 assays showed the highest robustness, independently of the pan-tau detector antibody targeting N-terminal or mid-region, and independently of the platform used. Considering the observed method disagreement in measured absolute concentrations, we stress the need for development of certified reference material, harmonizing measurements across different platforms.