Multiplex immunoassay measurement of amyloid-β to amyloid-β ratio in plasma discriminates between dementia due to Alzheimer's disease and dementia not due to Alzheimer's disease.

The cerebrospinal fluid (CSF) biomarkers amyloid-β (Aβ), total Tau, and phospho-181-Tau represent important diagnostic tools to support the clinical diagnosis of Alzheimer's disease (AD). Acquiring CSF by lumbar puncture is considered a moderately invasive procedure, while blood sampling is minimally invasive with calculable risks and can be performed by trained non-medical staff. Thus, the identification of reliable and robust blood biomarkers of AD-related neuropathology would be significantly advantageous in daily practice and would allow more patients to be screened. In this study, we performed a multiplex amyloid-β assay to simultaneously measure Aβ and Aβ. We analyzed how well Aβ, Aβ, and the Aβ to Aβ ratio (Aβ) could differentiate between patients suffering from dementia either due or not due to AD. In addition, we studied different factors affecting Aβ levels in plasma. Plasma Aβ level was significantly lower in patients with dementia due to AD than in those with dementia due to other causes. Aβ correlated weakly between plasma and CSF, but did not differ between amyloid-PET positive or negative patients. Furthermore, we found that kidney function influences Aβ and Aβ plasma levels, but not Aβ level. Liver function, age, and sex do not affect Aβ levels in plasma.