Performance characteristics of plasma amyloid-β 40 and 42 assays

Identifying biomarkers of Alzheimer's disease (AD) risk will be critical to effective AD prevention. Levels of circulating amyloid-β (Aβ) 40 and 42 may be candidate biomarkers. However, properties of plasma Aβ assays must be established. Using five different protocols, blinded samples were used to assess: intra-assay reproducibility; impact of EDTA vs. heparin anticoagulant tubes; and effect of time-to-blood processing. In addition, percent recovery of known Aβ concentrations in spiked samples was assessed. Median intra-assay coefficients of variation for the assay protocols ranged from 6-24% for Aβ40, and 8-14% for Aβ42. There were no systematic differences in reproducibility by collection method. Plasma concentrations of Aβ (particularly Aβ42) appeared stable in whole blood kept in ice packs and processed as long as 24 hours after collection. Recovery of expected concentrations was modest, ranging from -24% to 44% recovery of Aβ40, and 17% to 61% of Aβ42. In conclusion, across five protocols, plasma Aβ40 and Aβ42 levels were measured with generally low error, and measurements appeared similar in blood collected in EDTA versus heparin. While these preliminary findings suggest that measuring plasma Aβ40 and Aβ42 may be feasible in varied research settings, additional work in this area is necessary.