Preanalytical Sample Handling and Sample Stability Testing for the Neurochemical Dementia Diagnostics

Article type: Research Article

Authors: Zimmermann, Rüdiger^a | Lelental, Natalia^a | Ganslandt, Oliver^b | Maler, Juan Manuel^a | Kornhuber, Johannes^a | Lewczuk, Piotr^{a; *}

Affiliations: [a] Department of Psychiatry and Psychotherapy, Universitätsklinikum Erlangen and Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany | [b] Department of Neurosurgery, Universitätsklinikum Erlangen and Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany

Correspondence: [*] Correspondence to: Prof. Dr. med. Piotr Lewczuk, Lab for Clinical Neurochemistry and Neurochemical Dementia Diagnostics, Department of Psychiatry and Psychotherapy, Schwabachanlage 6, 91054 Erlangen, Germany. Tel.: +49 9131 85 34324; Fax: +49 9131 85 34238; E-mail: Piotr.Lewczuk@uk-erlangen.de.

Abstract: Preanalytical sample handling and storage procedures play an extremely important role in reliably measuring neurochemical dementia diagnostics (NDD) biomarkers: Aβ1-40, Aβ1-42, Tau, and pTau181. To test different handling and storage conditions, the following protocols were applied: (a) storage at room temperature for one week, (b) deep-freezing and thawing up to three cycles, (c) deep-freezing, thawing and keeping under +4°C for two days before the analysis, and (d) long-term stability of a deeply frozen sample. Between the first and the seventh day of the storage at room temperature, the percentage of the concentrations (compared to the starting concentrations) fluctuated: 104.3–105.3, 97.6–93.2, 100.6–96.8, and 97.9–90.2 for Aβ1-40, Aβ1-42, Tau, and pTau181, respectively. Re-freezing cycles resulted in the percentage fluctuations of the concentrations: 101.1–105.5, 95.4–99.7, 98.3–100.0, and 100.5–101.4 for Aβ1-40, Aβ1-42, Tau, and pTau181, respectively. Keeping previously frozen/thawed samples under +4°C for two days resulted in the percentage differences of the concentrations: +15.9, +2.2, −1.1, and −0.1 for Aβ1-40, Aβ1-42, Tau, and pTau181, respectively. During long-term stability, the coefficients of linear correlation (R2) were: Aβ1-40, 0.007; Aβ1-42, 0.02; Tau, 0.011; and pTau181, 0.02, and the corresponding inter-assay coefficients of variation: 13.9%, 13.9%, 11.0%, and 10.7% for Aβ1-40, Aβ1-42, Tau, and pTau181, respectively. We conclude that the NDD biomarkers are relatively stable when the cerebrospinal fluid sample is kept at room temperature for about four days; one or two thawing/refreezing cycles do not profoundly affect the biomarkers concentrations, however three cycles result in increased unsystematic variation. The four biomarkers seem to be stable in a sample stored deeply frozen for more than two years.

Keywords: Alzheimer's disease, amyloid-β, cerebrospinal fluid, laboratory quality control, preanalytical sample handling, Tau

DOI: 10.3233/JAD-2011-110212

Journal: Journal of Alzheimer's Disease, vol. 25, no. 4, pp. 739-745, 2011