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

Introduction We aimed to investigate factors defining amyloid β (1–42) (Aβ_1–42) adsorption during preanalytical workup of cerebrospinal fluid (CSF). Methods CSF was transferred to new tubes ≤4 times. Variables tested were different polypropylene tube brands, volumes, CSF Aβ_1–42 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. Results In diagnostic practice, the number of transfers varied between 1 and 3. Every tube transfer resulted in 5% loss of Aβ_1–42 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 Aβ_1–40 was similar, resulting in stable Aβ_1–42/Aβ_1–40 ratios over multiple tube transfers. Discussion We confirmed that adsorption of CSF Aβ_1–42 during preanalytical processing is an important confounder. However, use of the Aβ_1–42/Aβ_1–40 ratio overcomes this effect and can therefore contribute to increased diagnostic accuracy.