The PrecivityAD™ test: Accurate and reliable LC-MS/MS assays for quantifying plasma amyloid beta 40 and 42 and apolipoprotein E proteotype for the assessment of brain amyloidosis
Kristopher M. Kirmess, Matthew R. Meyer, Mary S. Holubasch, S Knapik, Yan Hu, Erin N. Jackson, Scott E. Harpstrite, Philip B. Verghese, Tim West, I. Fogelman, Joel B. Braunstein, Kevin E. Yarasheski, John H. Contois
Abstract
Background There is an unmet need for an accessible, less invasive, cost-effective method to facilitate clinical trial enrollment and aid in clinical Alzheimer’s disease (AD) diagnosis. APOE genotype affects the clearance and deposition of amyloid-beta (Aβ) with APOE 4 carriers having increased risk while APOE 2 alleles appear to be protective. Lower plasma Aβ42/40 correlates with brain amyloidosis. In response, C 2 N has developed the PrecivityAD™ test; plasma LC-MS/MS assays for Aβ isoform quantitation and qualitative APOE isoform-specific proteotyping. Methods In accord with CLIA standards, we developed and validated assay performance: precision, accuracy, linearity, limit of detection (LoD), interferences. RESULTS. Within-day precision varied from 1.5–3.0% (Aβ40) and 2.5–8.4% (Aβ42). Total (within-lab) variability was 2.7–7.7% (Aβ40) and 3.1–9.5% (Aβ42). Aβ40 quantitation was linear from 10 to 1780 pg/mL; Aβ42 was linear from 2 to 254 pg/mL. LoD was 11 and 2 pg/mL for Aβ40 and Aβ42, respectively. APOE proteotypes were 100% concordant with genotype, while LoD (fM) was much lower than APOE concentrations observed in plasma (mM). CONCLUSIONS. The PrecivityAD™ assays are precise, accurate, sensitive, and linear over a wide analytical range, free from significant interferences, and suitable for use in the clinical laboratory.