Investigation of the Number of Tests Required for Assaying Plasma Biomarkers Associated with Alzheimer's Disease Using Immunomagnetic Reduction.

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. 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). 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%. 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.