COMPARISON OF A FULLY AUTOMATED BEAD-BASED SYSTEM WITH AN ENZYME-LINKED IMMUNOSORBENT ASSAY AND AN ELECTROCHEMILUMINESCENT ASSAY FOR MEASUREMENT OF CORE AD BIOMARKERS

The CSF biomarkers beta-amyloid (Aβ) 1–40 and 1-42, p-tau, and t-tau are used in research to categorize Alzheimer's disease (AD) and in the clinical setting where they offer support for the diagnosis of AD. Compared to Ab42 the Ab42/Aβ40 ratio provides better diagnostic accuracy for cerebral Aβ pathology. Standard tests for analyzing these biomarkers are immunochemical assays such as INNOTEST (Aβ1-42, p-tau and t-tau) and Mesoscale Discovery (MSD, Aβ42/Aβ40). These methods are to a greater extent manual, involving several handling steps and incubation periods. As the importance of biomarkers increases, there is a need for reliable and robust methods. Lumipulse G-series is a fully automated system provided by Fujirebio that can analyze all four routine CSF biomarkers of AD in one instrument. Lumipulse uses single-analyte, ready-to-use, immunoreaction cartridges and renders quantitative results for an analyte within approximately 30 minutes. In Lumipulse, well-established sets of monoclonal antibodies are used in the assay set-up for capturing (magnetic particle) and detection of the specific analytes. The detection antibodies for Aβ1-42 and t-tau are biotinylated, whereas the ones for Aβ1-40 and p-tau are directly labeled with alkaline phosphatase. Substrate is added and the resulting concentration is measured. Between each addition a washing step occurs. Patient samples of CSF from clinical routine were used for method comparison. Lumipulse G assays were compared with INNOTEST® for Aβ1-42, p-tau and t-tau, and MSD for Aβ42/Aβ40. The inter-lab variation of Lumipulse was compared by using data from the Alzheimer's Association Quality Control program. Lumipulse showed good correlation with INNOTEST for Aβ1-42 (r=0.838), t-tau (r=0.874), and p-tau (r=0.966) and a slight positive bias for all biomarkers tested. This method also gave good correlation with MSD for the Aβ42:Aβ40 quotient (r=0.971). We reported on inter-lab variation on Aβ1-42 for 4 rounds on a longitudinal sample. Lumipulse G is a fully automated system that analyses the standard biomarkers of AD and correlates well with previously established methods. It also shows good inter-lab reproducibility. Method-specific reference values and decision limits need to be established.