Validation of soluble APP assays as diagnostic CSF biomarkers for neurodegenerative diseases
Waalwijk van Doorn, van, Linda J.C.
Koel-Simmelink, Marleen J.
Faculty of Pharmaceutical, Biomedical and Veterinary Sciences . Biomedical Sciences
Journal of neurochemistry. - Oxford
, p. 112-121
University of Antwerp
Background Analytical validation of a biomarker assay is essential before implementation in clinical practice can occur. In this study, we analytically validated the performance of assays detecting soluble amyloid-β precursor protein (sAPP) α and β in CSF in two laboratories according to previously SOPs serving this goal. Methods sAPPα and sAPPβ ELISA assays from two vendors (IBL, MSD) were validated. The performance parameters included precision, sensitivity, dilutional linearity, recovery and parallelism. Inter-laboratory variation, biomarker comparison (sAPPα versus sAPPβ) and clinical performance was determined in three laboratories using 60 samples of patients with subjective memory complaints, Alzheimer's disease or frontotemporal dementia. Results All performance parameters of the assays were similar between labs and within predefined acceptance criteria. The only exceptions were minor out-of-range results for recovery at low concentrations and, despite being within predefined acceptance criteria, non-comparability of the results for evaluation of the dilutional linearity and hook-effect. Based on the inter-laboratory correlation between Lab #1 and Lab #2, the IBL assays were more robust (sAPPα: r2=0.92, sAPPβ: r2=0.94) than the MSD assay (sAPPα: r2=0.70, sAPPβ: r2=0.80). Specificity of assays was confirmed using assay-specific peptide competitors. Clinical validation showed consistent results across the clinical groups in the different laboratories for all assays. Conclusion The validated sAPP assays appear to be of sufficient technical quality and perform well. Moreover, the study shows that the newly developed SOPs provide highly useful tools for the validation of new biomarker assays. A recommendation was made for renewed instructions to evaluate the dilutional linearity and hook-effect.