Plasma amyloid-β oligomers level is a biomarker for Alzheimer's disease diagnosis

► Plasma Aβ oligomers level is higher in AD patients compared to non-demented controls. ► Highest tertile of plasma Aβ oligomers independently associated with increased AD risk. ► Plasma Aβ oligomers level negatively correlated with cognition in AD. ► Plasma Aβ oligomers level: an useful biomarker for AD diagnosis.