Plasma Amyloid-β Forms in Alzheimer's Disease and Non-Alzheimer's Disease Patients

The objective of this study was to evaluate the diagnostic performance of full-length and N-truncated plasma amyloid-β (Aβ) forms in patients with Alzheimer's disease (AD) and non-Alzheimer's disease dementia (non-AD) as compared to healthy control subjects. Plasma samples from 50 AD, 50 non-AD, and 47 control subjects were included and analyzed using a multiparameter fluorimetric bead-based immunoassay for the simultaneous quantification of different Aβ forms. No significant differences in Aβ isoforms were detected between dementia and controls; or AD, non-AD, and controls. Compared to control subjects, pooled dementia patients (AD and non-AD) and AD patients alone had significantly lower plasma Aβ_1-42/Aβ_N-42 ratios. In each diagnostic group, all plasma Aβ concentrations were significantly correlated. No significant correlations between plasma Aβ forms and age were found. The low diagnostic performance of cross-sectional plasma Aβ measurements hampers future application as diagnostic markers or screening tools for dementia. CSF biomarker analysis remains superior, although the possible application of longitudinal plasma Aβ measurements as screening tools for dementia remains to be elucidated.