Plasma p‐tau181/Aβ <sub>1‐42</sub> ratio predicts Aβ‐PET status and correlates with CSF‐p‐tau181/Aβ <sub>1‐42</sub> and future cognitive decline
Christopher Fowler, Erik Stoops, Stephanie R. Rainey‐Smith, Eugeen Vanmechelen, Jeroen Vanbrabant, Nele Dewit, Kimberley Mauroo, Paul Maruff, Christopher C. Rowe, Jürgen Fripp, Qiao‐Xin Li, Pierrick Bourgeat, Steven Collins, Ralph N. Martins, Colin L. Masters, James D. Doecke
Abstract
Abstract Background In Alzheimer's disease (AD), plasma amyloid beta (Aβ) 1‐42 and phosphorylated tau (p‐tau) predict high amyloid status from Aβ positron emission tomography (PET); however, the extent to which combination of these plasma assays can predict remains unknown. Methods Prototype Simoa assays were used to measure plasma samples from participants who were either cognitively normal (CN) or had mild cognitive impairment (MCI)/AD in the Australian Imaging, Biomarkers and Lifestyle (AIBL) study. Results The p‐tau181/Aβ 1‐42 ratio showed the best prediction of Aβ‐PET across all participants (area under the curve [AUC] = 0.905, 95% confidence interval [CI]: 0.86–0.95) and in CN (AUC = 0.873; 0.80–0.94), and symptomatic (AUC = 0.908; 0.82–1.00) adults. Plasma p‐tau181/Aβ 1‐42 ratio correlated with cerebrospinal fluid (CSF) p‐tau181 (Elecsys, Spearman's ρ = 0.74, P < 0.0001) and predicted abnormal CSF Aβ (AUC = 0.816; 0.74–0.89). The p‐tau181/Aβ 1‐42 ratio also predicted future rates of cognitive decline assessed by AIBL Preclinical Alzheimer Cognitive Composite or Clinical Dementia Rating Sum of Boxes ( P < 0.0001). Discussion Plasma p‐tau181/Aβ 1‐42 ratio predicted both Aβ‐PET status and cognitive decline, demonstrating potential as both a diagnostic aid and as a screening and prognostic assay for preclinical AD trials.