Amyloid β peptides are differentially vulnerable to preanalytical surface exposure, an effect incompletely mitigated by the use of ratios

INTRODUCTION: We tested the hypothesis that the amyloid β (Aβ) peptide ratios are more stable than Aβ(42) alone when biofluids are exposed to two preanalytical conditions known to modify measurable Aβ concentration. METHODS: Human cerebrospinal fluid (CSF) and culture media (CM) from human cortical neurons were exposed to a series of volumes and polypropylene surfaces. Aβ(42), Aβ(40), and Aβ(38) peptide concentrations were measured using a multiplexed electrochemiluminescence immunoassay. Data were analyzed using mixed models in R. RESULTS: Decrease of measurable Aβ peptide concentrations was exaggerated in longer peptides, affecting the Aβ(42):Aβ(40) and Aβ(42):Aβ(38) ratios. However, the effect size of surface treatment was reduced in Aβ peptide ratios versus Aβ(42) alone. For Aβ(42):Aβ(40), the effect was reduced by approximately 50% (volume) and 75% (transfer) as compared to Aβ(42) alone. DISCUSSION: Use of Aβ ratios, in conjunction with concentrations, may mitigate confounding factors and assist the clinical diagnostic process for Alzheimer's disease.