Fully automated chemiluminescence enzyme immunoassays showing high correlation with immunoprecipitation mass spectrometry assays for β-amyloid (1-40) and (1-42) in plasma samples.

Blood based β-amyloid (Aβ) assays that can predict amyloid positivity in the brain are in high demand. Current studies that utilize immunoprecipitation mass spectrometry assay (IP-MS), which has high specificity for measuring analytes, have revealed that precise plasma Aβ assays have the potential to detect amyloid positivity in the brain. In this study, we developed plasma Aβ40 and Aβ42 immunoassays using a fully automated immunoassay platform that is used in routine clinical practice. Our assays showed high sensitivity (limit of quantification: 2.46 pg/mL [Aβ40] and 0.16 pg/mL [Aβ42]) and high reproducibility within-run (coefficients of variation [CVs]: <3.7% [Aβ40] and <2.0% [Aβ42]) and within-laboratory (CVs: <4.6% [Aβ40] and <5.3% [Aβ42]). The interference from plasma components was less than 10%, and the cross-reactivity with various lengths of Aβ peptides was less than 0.5%. In addition, we found a significant correlation between the IP-MS method and our immunoassay (correlation coefficients of Pearson's r: 0.91 [Aβ40] and 0.82 [Aβ42]). Our new method to quantify plasma Aβ40 and Aβ42 provides clinicians and patients with a way to continuously monitor disease progression.