properties of these proteins and the interference of matrix components make the establishment of reference materials very challenging. As a consequence up to now, the trust in the in commercial assays is limited. Since CSF quality control samples were not broadly available. Methods: A large number of individual CSF samples were pooled to establish 5 samples with different A b 1-42 and Ab 1-40 concentrations. Different compounds were added to the pools before lyophilization. The pools underwent one freeze-thaw cycle before aliquotation (250 ml, polypropylene screw-cap tubes). All aliquots were lyophilized and stored at -20 C. The consistency and homogeneity of the prepared panel was evaluated using three different lot numbers of the assays and analysis in 3 different laboratories by different users. In addition, the performance of the proficiency panel was integrated into a multicenter study and compared to performances of neat CSF or run-validation samples (¼ analyte in buffer). Results: Addition of components do not affect analytical behavior of the CSF sample. Lyophilisation of the samples was successful. Stability was considerably increased by that procedure as analytes showed only 5% CV after one week at 37 C. Neat CSF, with and without the additives, as well as samples from the proficiency panel, showed a very good parallelism (¼ absence of matrix interference in the assays) upon dilution for the three analytes evaluated in the study. The production process did not change the intrinsic characteristics of the CSF samples. Overall variability in a multicenter study for the proficiency panel did not exceed > 10%, including the sum of % CV of intra-run, inter-run, inter-operator, and inter-lab. Conclusions: A panel of 5 stabilized and lyophilized CSF samples with target values covering the whole range of the calibration curve of the A b 1-42 , Ab 1-40 and Total-Tau ELISA. The excellent precision data obtained in a multicenter study make this panel an excellent new tool to verify the quality of the biomarker measurements in research settings, but also for routine labs. In the absence of an international reference standard, this commercially available proficiency panel may significantly increase the trust in the values measured by ELISA of CSF diagnostics.
BackgroundCurrent research indicates that plasma β‐amyloid1‐42/β‐amyloid1‐40 ratio has the potential for application in clinical settings and clinical trials to predict brain β‐amyloid burden. It could reduce the number of lumbar punctures (for CSF biomarker testing) or Aβ‐PET scans in light of clinical trial recruitment and could serve as a tool to evaluate target engagement and efficacy of disease‐modifying drugs. The aim of the current study was to demonstrate the analytical performance of the newly developed Lumipulse G β‐Amyloid 1‐40 Plasma and Lumipulse G β‐Amyloid 1‐42 Plasma RUO assays.MethodThe LUMIPULSE G system is a chemiluminescent enzyme immunoassay platform enabling fully automated processing of samples using ready‐to‐use immunoreaction cartridges. Time to result in these single use test cartridges takes about 30 minutes. The analytical performance of the newly developed Lumipulse G β‐Amyloid 1‐40 Plasma and Lumipulse G β‐Amyloid 1‐42 Plasma RUO assays (using respectively 2G3 and 21F12 antibody for capturing and 3D6 antibody ALP‐conjugate for detection; two‐step immunoassay method) was determined. Parameters analysed were precision, sensitivity, linearity, and potential impact of interfering substances. The studies included a series of buffer‐ and K2EDTA plasma‐based samples at different concentration levels, each tested in several replicates (70 µL/replicate (Aβ1‐40); 110 µL/replicate (Aβ1‐42)) sized to the different parameters tested.ResultThe total within‐lab variability of both assays was ≤6 % CV confirming high precision of the LUMIPULSE G system. Using low β‐amyloid concentrated plasma samples, the observed LoD was 0.44 pg/mL (Aβ1‐40) and 0.37 pg/mL (Aβ1‐42), and the LoQ was 0.44 pg/mL (Aβ1‐40) and 0.43 pg/mL (Aβ1‐42). Linearity was shown across the assay range (0 – 5000 pg/mL (Aβ1‐40); 0 – 1000 pg/mL (Aβ1‐42)). No significant impact of commonly tested endogenous substances (bilirubin, chyle, triglycerides, rheumatoid factor (RF) and human anti‐mouse antibodies (HAMA)) was observed, except for haemoglobin.ConclusionThe analytical performance studies demonstrate – amongst other characteristics – low variability and high sensitivity enabling measurement of Aβ1‐40 and Aβ1‐42 in plasma. The Lumipulse G β‐Amyloid 1‐40 Plasma and Lumipulse G β‐Amyloid 1‐42 Plasma RUO assays are now ready to be explored further for clinical utility in various contexts of use.
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