Differences in Alzheimer's disease blood biomarker stability: Implications for the use of tau/amyloid ratios

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Abstract
INTRODUCTION: We compare the stability of phosphorylated tau (p‐tau)217, amyloid beta (Aβ)42, Aβ40, Aβ42/40, and p‐tau217/Aβ42 at different storage temperatures.METHODS: Ten ethylenediaminetetraacetic acid–plasma sample aliquots stored at frozen, refrigerated, and ambient temperatures were tested at various timepoints up to 30 days. The mean percent change from baseline was calculated.RESULTS: Aβ42 and Aβ40 concentrations decreased by >15% after 6 hours at ambient temperature and after 24 hours refrigerated, while p‐tau217 remained stable over 72 hours with < 10% deviation from baseline at either storage temperature. The Aβ42/40 ratio remained relatively constant as each analyte concentration decreased concurrently, while the p‐tau217/Aβ42 ratio deviated from baseline over time. All biomarkers were stable up to 30 days frozen.DISCUSSION: Differences in the stability of Aβ42 and p‐tau217 may lead to altered p‐tau217/Aβ42 ratio results if samples are not handled properly during the pre‐analytical testing phase. Ideally, samples should be frozen promptly and sent to the laboratory frozen.Highlights: Plasma phosphorylated tau (p‐tau)217, amyloid beta (Aβ)42, Aβ40, Aβ42/40, and p‐tau217/Aβ42 stability was assessed. P‐tau217 was stable, but Aβ42 and Aβ40 started decreasing by 6 hours at ambient temperature. The analyte stability differences led to falsely increased p‐tau217/Aβ42 ratios. Increases > 15% were seen in p‐tau217/Aβ42 after 6 hours at ambient temperature or 24 hours at 4°C.

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