Preanalytical stability of plasma/serum brain-derived tau.

INTRODUCTION: We investigated the effects of matrix type and reagent batch changes on diagnostic performances and longitudinal trajectories of brain-derived tau (BD-tau). METHODS: We evaluated (i) Cohort 1: paired EDTA plasma and serum from Alzheimer biomarker-positive older adults versus controls (n = 26); and (ii) Cohort 2: n = 79 acute ischemic stroke patients with 265 longitudinal samples across four time points. RESULTS: In Cohort 1, plasma and serum BD-tau were strongly correlated (rho = 0.96, p < 0.0001) with similar diagnostic performances (AUCs >99%) and correlations with CSF total-tau (rho = 0.93-0.94, p < 0.0001). However, absolute concentrations were ∼40% higher in plasma versus serum. In Cohort 2, first and repeated BD-tau measurements showed a near-perfect correlation (rho = 0.96, p < 0.0001), with no significant between-batch concentration differences. In longitudinal analyses, substituting ∼10% of the first-run concentrations for the remeasured values showed overlapping estimated trajectories without significant differences at any time point. DISCUSSION: BD-tau has equivalent diagnostic accuracies, but non-interchangeable absolute concentrations, in plasma versus serum. Furthermore, the analytical robustness is unaffected by batch-to-batch reagent variations. HIGHLIGHTS: Brain-derived tau (BD-tau) is a novel blood-based biomarker that quantifies tau protein of CNS origin. Effects of preanalytical handling procedures on the quality and reproducibility of BD-tau measures are unknown. In two cohorts of n = 105 participants, we compared BD-tau concentrations and diagnostic performances in paired plasma and serum samples, and evaluated impacts of batch-to-batch reagent variations. Paired plasma and serum showed equivalent diagnostic performances to separate amyloid-positive AD from amyloid-negative controls, indicating both can be used independently. Repeated measurements and longitudinal trajectories of plasma BD-tau were unaffected by batch-to-batch reagent variation.