Abstract
INTRODUCTION: An Elecsys® Amyloid β (Aβ [1-42]) immunoassay cutoff for classification of patients with Alzheimer's disease was investigated. METHODS: Cerebrospinal fluid samples collected from patients with mild-to-moderate Alzheimer's disease were analyzed by Elecsys® immunoassays: (1) Aβ (1-42), (2) total tau, and (3) phosphorylated tau. Cutoffs (Aβ [1-42] and ratios with tau) were estimated by method comparison between AlzBio3 (n = 206), mixture modeling (n = 216), and concordance with florbetapir F 18 imaging-based classification (n = 75). RESULTS: A 1065-pg/mL (95% confidence interval: 985-1153) Elecsys® Aβ (1-42) cutoff provided 94% overall percentage agreement with AlzBio3. Comparable cutoff estimates (95% confidence interval) were derived from mixture modeling (equally weighted: 1017 [949-1205] pg/mL; prevalence weighted: 1172 [1081-1344] pg/mL) and concordance with florbetapir F 18 imaging (visual read: 1198 [998-1591] pg/mL; automated: 1198 [1051-1638] pg/mL). DISCUSSION: Based on three approaches, a 1100-pg/mL Elecsys® Aβ (1-42) cutoff is suitable for clinical trials with similar populations and preanalytical handling.