INTRODUCTION: This study aimed to investigate the differential roles of various plasma biomarkers in a stepwise diagnostic strategy for Alzheimer's disease (AD). METHODS: A total of 2984 participants, including 666 cognitively unimpaired (CU), 2032 with Alzheimer's clinical syndrome (ACS), and 286 non-ACS individuals, were recruited. Plasma amyloid beta (Aβ) 42/40, four phosphorylated tau (p-tau) epitopes, glial fibrillary acidic protein (GFAP), and neurofilament light chain (NfL) levels were measured using immunoassays. RESULTS: NfL demonstrated fair to excellent accuracy in differentiating non-ACS from CU groups (area under the curve [AUC], 0.79 to 0.94). p-tau217 had the highest accuracy for identifying Aβ (AUC 0.94) and tau positron emission tomography status (AUC 0.91). In the ACS group, p-tau217 was the strongest predictor of cognitive decline (p <
.001). DISCUSSION: NfL may serve as a useful screening tool, while p-tau217 is particularly valuable for confirming AD pathology and prognosis. HIGHLIGHTS: Plasma NfL could screen for cognitive impairment. p-tau217 reliably detects AD pathology, regardless of diagnosis. p-tau217 and GFAP predict prognosis in ACS. Each plasma biomarker plays a distinct role in stepwise AD diagnostics.