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Preclinical prediction of Alzheimer disease (AD) is important and critical to effective intervention. Plasma levels of amyloid-β (Aβ) peptides have been a principal focus of the growing literature on blood-based biomarkers, but studies to date have varied in design, assay methods, and sample size, making it difficult to readily interpret the overall data.

To conduct a systematic review and meta-analysis of relevant prospective studies to determine whether plasma amyloid-β levels may predict development of dementia, AD, and cognitive decline.

We searched prospective studies published between 1995 and 2011 indexed in the MEDLINE, EMBASE, and PsycINFO databases. Selected studies included those measuring at least 1 relevant plasma amyloid-β species (Aβ₄₀, Aβ₄₂, or Aβ₄₂:Aβ₄₀ ratio) and reporting an effect estimate for dementia, AD, or cognitive change.