How to handle adsorption of cerebrospinal fluid amyloid β (1–42) in laboratory practice? Identifying problematic handlings and resolving the issue by use of the Aβ42/Aβ40 ratio

Abstract

IntroductionWe aimed to investigate factors defining amyloid β (1–42) (Aβ1–42) adsorption during preanalytical workup of cerebrospinal fluid (CSF). MethodsCSF was transferred to new tubes ≤4 times. Variables tested were different polypropylene tube brands, volumes, CSF Aβ1–42 concentrations, incubation times, pipettes, vortex intensities, and other CSF proteins, including hyperphosphorylated tau and Interleukin 1 Receptor Accessory Protein (IL-1RAcP). An enquiry assessed the number of transfers in current practice. ResultsIn diagnostic practice, the number of transfers varied between 1 and 3. Every tube transfer resulted in 5% loss of Aβ1–42 concentration, even 10% in small volumes. Adsorption was observed after 30 seconds and after contact with the pipette tip. Tube brand, vortexing, or continuous tube movement did not influence adsorption. Adsorption for Aβ1–40 was similar, resulting in stable Aβ1–42/Aβ1–40 ratios over multiple tube transfers. DiscussionWe confirmed that adsorption of CSF Aβ1–42 during preanalytical processing is an important confounder. However, use of the Aβ1–42/Aβ1–40 ratio overcomes this effect and can therefore contribute to increased diagnostic accuracy.