Effects of storage conditions on the stability of blood-based markers for the diagnosis of Alzheimer's disease

Objectives: Alzheimer's disease (AD) is considered the most common cause of dementia in older people. Recently, blood-based markers (BBM) A beta 1-42, A beta 1-40, and phospho Tau181 (p-Tau181) have demonstrated the potential to transform the diagnosis and prognostic assessment of AD. Our aim was to investigate the effect of different storage conditions on the quantification of these BBM and to evaluate the interchangeability of plasma and serum samples. Methods: Forty-two individuals with some degree of cognitive impairment were studied. Thirty further patients were retrospectively selected. A beta 1-42, A beta 1-40, and p-Tau181 were quantified using the LUMIPULSE-G600II automated platform. To assess interchangeability between conditions, correction factors for magnitudes that showed strong correlations were calculated, followed by classification consistency studies. Results: Storing samples at 4 degrees C for 8-9 days was associated with a decrease in A beta fractions but not when stored for 1-2 days. Using the ratio partially attenuated the preanalytical effects. For p-Tau181, samples stored at 4 degrees C presented lower concentrations, whereas frozen samples presented higher ones. Concerning classification consistency in comparisons that revealed strong correlations (p-Tau181), the percentage of total agreement was greater than 90% in a large number of the tested cut-offs values. Conclusions: Our findings provide relevant information for the standardization of sample collection and storage in the analysis of AD BBM in an automated platform. This knowledge is crucial to ensure their introduction into clinical settings.