Pérez-Grijalba V, Arbizu J, Romero J, et al. – Researchers assessed 39 cognitively normal individuals and 20 patients with mild cognitive impairment from the AB255 Study to investigate the link between plasma amyloid-beta (Aβ) levels and the presence of pathological accumulation of Aβ in the brain measured by amyloid-PET. They evaluated both plasma Aβ42/40 ratio alone or combined with an FDG-PET-based biomarker of neurodegeneration as potential Alzheimer disease biomarkers. Study participants who had undergone PiB-PET scans were included. Using ABtest kits, total Aβ40 and Aβ42 levels in plasma (TP42/40) were quantified. Overall, 18 individuals were Aβ-PET–positive. Aβ-PET status with an area under the curve (AUC) of 0.881 was identified by TP42/40 alone. In addition, the most accurate Aβ-PET predictor with an AUC of 0.965 was the combination of both FDG-PET scores and plasma Aβ biomarkers. In preclinical and prodromal stages of Alzheimer disease, plasma TP42/40 ratio exhibited a relevant and significant potential as a screening tool to identify brain Aβ positivity.