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.