Scientific Poster - In an Optimized CSF Collection Protocol the pTau181/Aβ1-42 Ratio Increases Preanalytical Variability Over Measuring Aβ1-42 Alone

Background

Core cerebrospinal fluid (CSF) biomarker concentrations for β-amyloid1-42 (Aβ1-
42), β-amyloid1-40 (Aβ1-40), and pTau181 are valuable in the diagnosis of
Alzheimer’s Disease (AD). Specifically, when used in a ratio Aβ1-42/Aβ1-40 and
pTau181/Aβ1-42 have shown high concordance with amyloid PET. However,
questions remain on the robustness of these ratios when used in clinical routine
due to the tendency of amyloid to adsorb to surfaces causing amyloid loss that may
result in misdiagnosis. Stringent handling procedures of CSF have been proposed
to reduce amyloid loss including the use of a single polypropylene tube type. The
proposal of a single tube complicates CSF collection and creates doubt in results
obtained from alternative tube types. In this study the effect of varying
polypropylene tube type within clinical routine on amyloid concentration using Aβ1-
42/Aβ1-40 and ptau181/Aβ1-42 ratios was evaluated in freshly collected CSF. The
utility of the ratios to correct for pre-analytical variability and bring concentrations
within +/- 5% of baseline as indicated by recently published Alzheimer’s
Association International Guidelines for CSF handling2 was examined.

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