Validation of the LUMIPULSE automated immunoassay for the measurement of core AD biomarkers in cerebrospinal fluid

Objectives The core cerebrospinal fluid (CSF) biomarkers; total tau (tTau), phospho-tau (pTau), amyloid beta 1-42 (A beta 1-42), and the A beta 1-42/A beta 1-40 ratio have transformed Alzheimer's disease (AD) research and are today increasingly used in clinical routine laboratories as diagnostic tools. Fully automated immunoassay instruments with ready-to-use assay kits and calibrators has simplified their analysis and improved reproducibility of measurements. We evaluated the analytical performance of the fully automated immunoassay instrument LUMIPULSE G (Fujirebio) for measurement of the four core AD CSF biomarkers and determined cutpoints for AD diagnosis. Methods Comparison of the LUMIPULSE G assays was performed with the established INNOTEST ELISAs (Fujirebio) for hTau Ag, pTau 181, beta-amyloid 1-42, and with V-PLEX Plus A beta Peptide Panel 1 (6E10) (Meso Scale Discovery) for A beta 1-42/A beta 1-40, as well as with a LC-MS reference method for A beta 1-42. Intra- and inter-laboratory reproducibility was evaluated for all assays. Clinical cutpoints for A beta 1-42, tTau, and pTau was determined by analysis of three cohorts of clinically diagnosed patients, comprising 651 CSF samples. For the A beta 1-42/A beta 1-40 ratio, the cutpoint was determined by mixture model analysis of 2,782 CSF samples. Results The LUMIPULSE G assays showed strong correlation to all other immunoassays (r>0.93 for all assays). The repeatability (intra-laboratory) CVs ranged between 2.0 and 5.6%, with the highest variation observed for beta-amyloid 1-40. The reproducibility (inter-laboratory) CVs ranged between 2.1 and 6.5%, with the highest variation observed for beta-amyloid 1-42. The clinical cutpoints for AD were determined to be 409 ng/L for total tau, 50.2 ng/L for pTau 181, 526 ng/L for beta-amyloid 1-42, and 0.072 for the A beta 1-42/A beta 1-40 ratio. Conclusions Our results suggest that the LUMIPULSE G assays for the CSF AD biomarkers are fit for purpose in clinical laboratory practice. Further, they corroborate earlier presented reference limits for the biomarkers.

Automated summary

The study evaluated the LUMIPULSE G assays for core cerebrospinal fluid biomarkers and established cutpoints for Alzheimer's disease diagnosis. Results showed strong correlation and reliable analytical performance of the LUMIPULSE G assays.