| Summary: | Abstract 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.
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