Cerebrospinal Fluid Aβ42/Aβ40 as a Means to Limiting Tube- and Storage-Dependent Pre-Analytical Variability in Clinical Setting

Background: Alzheimer's disease (AD) cerebrospinal fluid (CSF) biomarkers have recently been included in the criteria for AD diagnosis. Unfortunately, their wider use in routine and interpretation require more standardization, particularly for the pre-analytical steps. In particular, amyloid-beta (A beta) 42 peptide measurement is strongly influenced by the type of collection tube and by repeated freeze/thaw cycles. Objective: The objectives of this study were to compare, in clinical setting, the impact of collection tubes and the repetition of freeze/thaw cycles on A beta(42) and A beta(40) concentrations and consequently determine if the A beta(42)/A beta(40) ratio could resolve the diagnosis difficulties related to these pre-analytical parameters. Methods: CSF from 35 patients was collected in different polypropylene (PP) and stored at -80 degrees C after sampling. For CSF collected in the reference tube, three successive freeze-thawcycles were done. A beta(42) and A beta(40) concentrations were determined in each condition in order to calculate the A beta(42)/A beta(40) ratio. Results: Our results showed that CSF A beta(42) and A beta(40) values were significantly different according to the type of collection tube and the number of freeze/thaw cycles. Although the calculation of the A beta(42)/A beta(40) ratio eliminated the effect of PP tube-dependent variation, this was not the case for freeze-thaw cycle-associated variation. Conclusion: The use of A beta(42)/A beta(40) ratio rather than A beta(42) alone could contribute toward pre-analytical standardization, thus allowing the general use of CSF AD biomarkers in routine practice.