Vergallo A, et al. - Blood-based biomarkers of pathophysiologic brain amyloid β (Aβ) accumulation, especially for preclinical targets and large-scale interventions, are needed to improve clinical trials and manage Alzheimer's disease effectivel, so researchers ascertained if plasma concentrations of the Aβ_1–40/Aβ_1–42 ratio, evaluated using the single-molecule array (Simoa) immunoassay, can predict brain Aβ positron emission tomography status. They included a large-scale longitudinal monocentric cohort (N = 276) of older individuals with subjective memory complaints for this purpose. For the Aβ_1–40/Aβ_1–42 plasma ratio, the receiver operating characteristic curve and machine learning showed a balanced accuracy of 76.5% and 81%, respectively. Apolipoprotein E (APOE) ε4 allele, sex, or age does not affect accuracy.