Performance Characteristics of Plasma Amyloid-beta 40 and 42 Assays

Identifying biomarkers of Alzheimer's disease (AD) risk will be critical to effective AD prevention. Levels of circulating amyloid-beta (A beta) 40 and 42 may be candidate biomarkers. However, properties of plasma A beta 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 A beta concentrations in spiked samples was assessed. Median intra-assay coefficients of variation for the assay protocols ranged from 6-24% for A beta(40), and 8-14% for A beta(42). There were no systematic differences in reproducibility by collection method. Plasma concentrations of A beta (particularly A beta(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 A beta(40), and 17% to 61% of A beta(42). In conclusion, across five protocols, plasma A beta(40) and A beta(42) 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 A beta(40) and A beta(42) may be feasible in varied research settings, additional work in this area is necessary.