Introduction: We studied the effect of long-term storage at -80°C on cerebrospinal fluid (CSF) biomarker levels. Our approach assumed consistency of mean biomarker levels in a homogenous Alzheimer's disease patient cohort over time.
Methods: We selected 148 Alzheimer's disease samples that had inclusion dates equally distributed over the years 2001 to 2013 from our biobank. The concentrations of CSF biomarkers, amyloid β1-42 (Aβ1-42), total tau (T-tau), and phosphorylated tau181 (P-tau), were measured with one enzyme-linked immunosorbent assay lot. Results were compared with historical results obtained at biobank inclusion.
Results: Linear regression analyses showed that the levels of CSF biomarkers, Aβ1-42, T-tau, and P-tau, were not related to storage time at -80°C (β = 0.015, 0.048, and 0.0016 pg/mL per day, not significant). However, the differences between remeasured concentrations of Aβ1-42 and concentrations at biobank inclusion measured for more than 30 assay batches increased with increasing time difference.
Discussion: The levels of CSF biomarkers, Aβ1-42, T-tau, and P-tau, did not significantly change during the maximum period of 12 years of storage at -80°C. Batch variation for Aβ1-42 is a factor that should be controlled for when using historical cohorts.
Keywords: Alzheimer's disease; Amyloid β1–42; Batch variation; Biomarkers; Cerebrospinal fluid; ELISA; Long-term storage; Phosphorylated tau181; Preanalytical variation; Total tau.