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 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, Aβ, and Aβ 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:Aβ and Aβ:Aβ ratios. However, the effect size of surface treatment was reduced in Aβ peptide ratios versus Aβ alone. For Aβ:Aβ, the effect was reduced by approximately 50% (volume) and 75% (transfer) as compared to Aβ alone.

Discussion: Use of Aβ ratios, in conjunction with concentrations, may mitigate confounding factors and assist the clinical diagnostic process for Alzheimer's disease.