Identifying biomarkers of Alzheimer 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 (CVs) for the assay protocols ranged from 6–24% for Aβ-40, and 8–14% for Aβ-42. There were no systematic differences in reproducibility by collection method. Plasma concentrations of Aβ (particularly Aβ-42) 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 Aβ-40, and 17% to 61% of Aβ-42.
Across five protocols, plasma Aβ-40 and Aβ-42 levels were measured with generally low error, and measurements appeared similar in blood collected in EDTA vs. heparin. While these preliminary findings suggest that measuring plasma Aβ-40 and Aβ-42 may be feasible in varied research settings, additional work in this area is necessary.