Introduction: Concentrations of plasma biomarkers associated with Alzheimer’s disease have been reported to be as low as several tens of picograms/milliliter (pg/ml). However, in assays measuring these biomarkers, it is likely that repeated measurements are necessary to obtain reliable values. Methods: We performed assays as a single test or as duplicate, quadruplicate, fivefold and tenfold repeated tests, on samples spiked with different concentrations of amyloid β 1–40 (Aβ1–40; 1–1000 pg/ml), Aβ1–42 (1–30,000 pg/ml) and total Tau protein (T-Tau; 0.1–1000 pg/ml), with the aim to to calculate the coefficients of variation (CVs). Results: The results demonstrated common changes in the CVs with changes in the number of tests for a given sample: the CVs decreased with increases in the number of tests from one to ten. All CV values were distributed within the range of 0.35 to 15.5%; as such, the CV values were all lower than the acceptable value of 20%. Conclusion: Based on this study, a single assay of Aβ1–40, Aβ1–42 and T-Tau, respectively, provides reliable results in terms of the measurement of that plasma biomarker.
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