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

Abstract 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.