Validation of a Commercial Chemiluminescence Immunoassay for the Simultaneous Measurement of Three Different Amyloid-beta Peptides in Human Cerebrospinal Fluid and Application to a Clinical Cohort

Acomprehensive assay validation campaign of a commercially available chemiluminescence multiplex immunoassay for the simultaneous measurement of the amyloid-beta peptides A beta(38), A beta(40), and A beta(42) in human cerebrospinal fluid (CSF) is presented. The assay quality parameters we addressed included impact of sample dilution, parallelism, lower limits of detection, lower limits of quantification, intra- and inter-assay repeatability, analytical spike recoveries, and between laboratory reproducibility of the measurements. The assay performed well in our hands and fulfilled a number of predefined acceptance criteria. The CSF levels of A beta(40) and A beta(42) determined in a clinical cohort (n = 203) were statistically significantly correlated with available ELISA data of A beta(1-40) (n = 158) and A beta(1-42) (n = 179) from a different laboratory. However, Bland-Altman method comparison indicated systematic differences between the assays. The data presented here furthermore indicate that the CSF concentration of A beta(40) can surrogate total CSF A beta and support the hypothesis that the A beta(42)/A beta(40) ratio outperforms CSF A beta(42) alone as a biomarker for Alzheimer's disease due to a normalization to total A beta levels.