Analytical and Clinical Validation of β-Amyloid 1-40, 1-42, and the 1-42/1-40 Ratio Using a Clinical Autoanalyzer
Ayla Harris1, Tien Le1, Bradley Collier1, Matthew Chappell1, Ahmed Chenna2, Youssouf Badal2, Bryan Lim2, Brandon Yee2, Christos Petropoulos2, John Winslow2, Deborah Boles1, Russell Grant1
1Research and Development, Labcorp, 2Monogram Biosciences Inc
Objective:
Validation of a high-throughput Aβ42/40 plasma assay.
Background:
PET imaging and measurements in CSF have been traditionally used to investigate the presence of β-amyloid plaques for diagnosis of Alzheimer’s disease (AD), but these approaches are costly and invasive1. As an alternative, plasma-based measurements are currently being investigated to broaden testing accessibility.
Design/Methods:
The Sysmex HISCL®-5000 Immunoassay System was used to validate immunoassays for the measurement of Aβ40 and Aβ42 in plasma samples to determine the Aβ42/40 ratio. Validation of these measurements included investigation of assay imprecision, analytical measurement range (AMR), common interferences as well as measurements of sample stability. In addition, clinically defined specimens2 were measured to determine an appropriate cutoff with respect to β-amyloid PET results. The Aβ42/40 ratio of clinically defined samples was also measured using assays from two predicate assays.
Results:
Imprecision results produced within-laboratory CVs ≤ 6.5% for both Aβ40, Aβ42, as well as the Aβ42/40 ratio. The AMR of each assay was found to be suitable for measurements of anticipated plasma concentrations and acceptable levels of common assay interferents were identified. Sample stability was demonstrated to allow appropriate shipping and handling of specimens. Clinically defined specimens were analyzed using receiver operator characteristic (ROC) analysis of the Aβ42/40 results with respect to β-amyloid status. Results produced an area under the curve (AUC) of 0.94 and a cutoff of 0.102. This cutoff produced a sensitivity and specificity of 96.0 and 86.7%, respectively, and is consistent with the manufacturer proposed cutoff3. Furthermore, the AUC observed for the existing commercial assays was ≤ 0.89.
Conclusions:
Measurement of Aβ42/40 in patient plasma samples using a high efficiency platform is now available to assist physicians with identifying patients with β-amyloid plaques and potentially the presence of Alzheimer’s disease.