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

Preanalytical sample handling and storage procedures play an extremely important role in reliably measuring neurochemical dementia diagnostics (NDD) biomarkers: A beta(1-40), A beta(1-42), 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 degrees 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 A beta(1-40), A beta(1-42), 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 A beta(1-40), A beta(1-42), Tau, and pTau181, respectively. Keeping previously frozen/thawed samples under +4 degrees C for two days resulted in the percentage differences of the concentrations: +15.9, + 2.2, -1.1, and -0.1 for A beta(1-40), A beta(1-42), Tau, and pTau181, respectively. During long-term stability, the coefficients of linear correlation (R(2)) were: A beta(1-40), 0.007; A beta(1-42), 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 A beta(1-40), A beta(1-42), 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.