Correlations of p‐tau217, p‐tau181 and tau levels between CSF and plasma that are measured by fully automated immunoassay platform

Abstract

AbstractBackgroundCerebrospinal fluid (CSF)‐based ATN classification (A: β‐amyloid (Aβ) deposition, T: pathogenic tau accumulation, N: neurodegeneration) is being widely accepted for the characterization of Alzheimer’s disease (AD). However, for the implementation of ATN classification in clinical practice, blood‐based biomarker is preferable in terms of specimen collection ease. Therefore, we have developed the blood‐based biomarker assays that correlate well with CSF levels. We have previously demonstrated that the plasma tau and phosphorylated tau at threonine‐181 (p‐tau181) immunoassays can significantly differentiate between AD, mild cognitive impairment (MCI), and cognitively normal (CN) groups. Here, we evaluated the correlation of biomarker levels between CSF and plasma utilizing the biomarker panel with addition of phosphorylated tau at threonine‐217 (p‐tau217) immunoassay.MethodWe have measured p‐tau217, p‐tau181 and tau using commercially available specimens on a fully automated immunoassay platform, HISCLTM analyzer. The platform can achieve high degree of sensitivity, requires only 30 µl of sample and 17 minutes to complete the measurement per assay. The bio‐analytical performance for the immunoassays was evaluated by measuring lower limit of quantification (LLOQ). The developed immunoassays were used to measure the paired CSF and plasma specimens from AD (n = 10), MCI (n = 35) and CN (n = 9) groups.ResultThe quantitative sensitivity for p‐tau217, p‐tau181 and tau were sufficient to measure plasma specimens in all groups. The plasma biomarker levels were significantly different between the AD and CN groups for all the biomarkers. We have found good correlations of biomarker levels between CSF and plasma for p‐tau217 (rs = 0.594, p < 0.01), p‐tau181 (rs = 0.453, p < 0.01) and tau (rs = 0.326, p < 0.05).ConclusionOur results indicated the possibility of detecting plasma p‐tau217, p‐tau181 and tau levels which may reflect the CSF levels. In addition to these assays, we have also developed plasma Ab and neurofilament light chain assays that had demonstrated good correlation with CSF levels. Thus, all the plasma assays developed on the HISCL analyzer could assess ATN classification. The blood‐based biomarker panel using our fully automated assay will accelerate research in the dementia field and may help in appropriate diagnosis of patients with dementia in routine clinical practice.