RESUMO
INTRODUCTION: Blood-based assays to measure brain amyloid beta (Aß) deposition are an attractive alternative to the cerebrospinal fluid (CSF)-based assays currently used in clinical settings. In this study, we examined different blood-based assays to measure Aß and how they compare among centers and assays. METHODS: Aliquots from 81 plasma samples were distributed to 10 participating centers. Seven immunological assays and four mass-spectrometric methods were used to measure plasma Aß concentrations. RESULTS: Correlations were weak for Aß42 while Aß40 correlations were stronger. The ratio Aß42/Aß40 did not improve the correlations and showed weak correlations. DISCUSSION: The poor correlations for Aß42 in plasma might have several potential explanations, such as the high levels of plasma proteins (compared to CSF), sensitivity to pre-analytical sample handling and specificity, and cross-reactivity of different antibodies. Different methods might also measure different pools of plasma Aß42. We, however, hypothesize that greater correlations might be seen in future studies because many of the methods have been refined during completion of this study.