Plasma Amyloid-beta 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-beta (A beta) 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 A beta forms. No significant differences in A beta 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 A beta(1-42)/A beta(N-42) ratios. In each diagnostic group, all plasma A beta concentrations were significantly correlated. No significant correlations between plasma A beta forms and age were found. The low diagnostic performance of cross-sectional plasma A beta measurements hampers future application as diagnostic markers or screening tools for dementia. CSF biomarker analysis remains superior, although the possible application of longitudinal plasma A beta measurements as screening tools for dementia remains to be elucidated.