No correlation between time-linked plasma and CSF Abeta levels.

Plasma beta-amyloid protein (Abeta) isoforms are considered potential biomarkers for Alzheimer's disease (AD) and dementia. The relation between plasma and cerebrospinal fluid (CSF) levels of Abeta isoforms remains unclear. In order to identify possible correlations between Abeta levels in plasma and CSF we determined Abeta levels in time-linked plasma and CSF samples. Abeta concentrations in plasma (Abeta(1-42) and Abeta(N-42)) and CSF (Abeta(1-42)) samples from 49 AD patients, 47 non-Alzheimer's disease dementia (NONAD) patients, 39 MCI patients and 29 controls were determined using a multi-parameter fluorimetric bead-based immunoassay using xMAP((R)) technology (for plasma) and a conventional single-parameter ELISA (for CSF). Plasma Abeta(1-42) concentrations did not correlate with CSF Abeta(1-42) concentrations in the total study population, or in the different diagnostic groups. No correlations between plasma Abeta(N-42) and CSF Abeta(1-42) levels were found either. The CSF/serum albumin index did not show any significant differences between AD, NONAD, MCI and controls. These results suggest that the Abeta levels in plasma are independent of the Abeta levels in CSF both in dementia and controls. The fact that CSF and plasma Abeta do not correlate in patients as well as controls and no significant differences in plasma Abeta(1-42) or Abeta(N-42) between patients and controls can be detected hampers the diagnostic utility of the plasma Abeta levels as biomarkers for dementia.