Influence of kidney function and CSF/serum albumin ratio on plasma Aβ42 and Aβ40 levels measured on a fully automated platform in patients with Alzheimer’s disease

Introduction Alzheimer's disease (AD) is characterized by decreased cerebrospinal fluid (CSF) A beta 42 and A beta 42/A beta 40 ratio. A beta peptides can now be measured also in plasma and are promising peripheral biomarkers for AD. We evaluated the relationships of plasma A beta species with their CSF counterparts, kidney function, and serum/CSF albumin ratio (Q-Alb) in AD patients.Materials and methods We measured plasma A beta 42 and A beta 40, as well as CSF AD biomarkers, with the fully automated Lumipulse platform in a cohort of N = 30 patients with clinical and neurochemical diagnosis of AD.Results The two plasma A beta peptides correlated strongly with each other ( r = 0.7449), as did the corresponding CSF biomarkers (r = 0.7670). On the contrary, the positive correlations of plasma A beta 42, A beta 40, and A beta 42/A beta 40 ratio with their CSF counterparts and the negative correlation of plasma A beta 42/A beta 40 ratio with CSF P-tau181 were not statistically significant. Plasma levels of both A beta species negatively correlated with estimated glomerular filtration rate (eGFR) (A beta 42: r = -0.4138; A beta 40: r = -0.6015), but plasma A beta 42/A beta 40 ratio did not. Q-Alb did not correlate with any plasma A beta parameter.Discussion Plasma A beta 42 and A beta 40 are critically influenced by kidney function; however, their ratio is advantageously spared from this effect. The lack of significant correlations between plasma A beta species and their CSF counterparts is probably mainly due to small sample size and inclusion of only A beta+ individuals. Q-Alb is not a major determinant of plasma A beta concentrations, highlighting the uncertainties about mechanisms of A beta transfer between CNS and periphery.