title: Validation of soluble amyloid-β precursor protein assays as diagnostic CSF biomarkers for neurodegenerative diseases.
abstract: 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 standard operating procedures serving this goal. sAPPα and sAPPβ ELISA assays from two vendors (IBL-international, Meso Scale Diagnostics) were validated. The performance parameters included precision, sensitivity, dilutional linearity, recovery, and parallelism. Inter-laboratory variation, biomarker comparison (sAPPα vs. sAPPβ) and clinical performance was determined in three laboratories using 60 samples of patients with subjective memory complaints, Alzheimer's disease, or frontotemporal dementia. 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-international assays were more robust (sAPPα: r(2) = 0.92, sAPPβ: r(2) = 0.94) than the Meso Scale Diagnostics (MSD) assay (sAPPα: r(2) = 0.70, sAPPβ: r(2) = 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. The validated sAPP assays appear to be of sufficient technical quality and perform well. Moreover, the study shows that the newly developed standard operating procedures 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. We analytically validated the performance of assays detecting soluble amyloid-β precursor protein (sAPP) α and β in CSF according to SOPs in agreement with ISO15189 guidelines. The validated sAPP assays appear to be of sufficient technical quality and perform well. Moreover, this study proofs that the newly developed SOPs, with a minor modification, provide highly useful tools for the validation of new biomarker assays.
authors.affiliation: Department of Neurology, Department of Laboratory Medicine, Radboud University Medical Center, Radboud Alzheimer Centre, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands.
authors.forename: Linda J C
authors.initials: LJ
authors.lastname: van Waalwijk van Doorn
authors.affiliation: Neurochemistry Laboratory and Biobank, Department of Clinical Chemistry, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Marleen J
authors.initials: MJ
authors.lastname: Koel-Simmelink
authors.affiliation: Department of Psychiatry and Psychotherapy, Faculty of Medicine, LVR-Hospital Essen, University of Duisburg-Essen, Essen, Germany.
authors.forename: Ute
authors.initials: U
authors.lastname: Haußmann
authors.affiliation: Department of Psychiatry and Psychotherapy, Faculty of Medicine, LVR-Hospital Essen, University of Duisburg-Essen, Essen, Germany.|Department of Psychiatry and Psychotherapy, University Medical Center Goettingen, Georg-August-University, Goettingen, Germany.
authors.forename: Hans
authors.initials: H
authors.lastname: Klafki
authors.affiliation: Reference Center for Biological Markers of Dementia (BIODEM), Institute Born-Bunge, University of Antwerp, Antwerp, Belgium.
authors.forename: Hanne
authors.initials: H
authors.lastname: Struyfs
authors.affiliation: Department of Chemistry, Technische Universität Dresden, Dresden, Germany.
authors.forename: Philipp
authors.initials: P
authors.lastname: Linning
authors.affiliation: Department of Chemistry, Technische Universität Dresden, Dresden, Germany.
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Knölker
authors.affiliation: Neurochemistry Laboratory and Biobank, Department of Clinical Chemistry, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Harry
authors.initials: H
authors.lastname: Twaalfhoven
authors.affiliation: Department of Neurology, Department of Laboratory Medicine, Radboud University Medical Center, Radboud Alzheimer Centre, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands.
authors.forename: H Bea
authors.initials: HB
authors.lastname: Kuiperij
authors.affiliation: Reference Center for Biological Markers of Dementia (BIODEM), Institute Born-Bunge, University of Antwerp, Antwerp, Belgium.|Memory Clinic and Department of Neurology, Hospital Network Antwerp (ZNA), Antwerp, Belgium.
authors.forename: Sebastiaan
authors.initials: S
authors.lastname: Engelborghs
authors.affiliation: Alzheimer Center VUmc, Amsterdam, The Netherlands.
authors.forename: Philip
authors.initials: P
authors.lastname: Scheltens
authors.affiliation: Department of Neurology, Department of Laboratory Medicine, Radboud University Medical Center, Radboud Alzheimer Centre, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands.
authors.forename: Marcel M
authors.initials: MM
authors.lastname: Verbeek
authors.affiliation: R&D, ADx NeuroSciences, Ghent, Belgium.
authors.forename: Eugeen
authors.initials: E
authors.lastname: Vanmechelen
authors.affiliation: Department of Psychiatry and Psychotherapy, University Medical Center Goettingen, Georg-August-University, Goettingen, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Wiltfang
authors.affiliation: Neurochemistry Laboratory and Biobank, Department of Clinical Chemistry, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Charlotte E
authors.initials: CE
authors.lastname: Teunissen
mesh_terms: D000544:Alzheimer Disease / Q000134:cerebrospinal fluid / Q000175:diagnosis; D016564:Amyloid beta-Protein Precursor / Q000134:cerebrospinal fluid*; D015415:Biomarkers / Q000134:cerebrospinal fluid; D004797:Enzyme-Linked Immunosorbent Assay; D057180:Frontotemporal Dementia / Q000134:cerebrospinal fluid / Q000175:diagnosis; D006801:Humans; D059021:Laboratory Proficiency Testing; D008569:Memory Disorders / Q000134:cerebrospinal fluid / Q000175:diagnosis; D019636:Neurodegenerative Diseases / Q000134:cerebrospinal fluid* / Q000175:diagnosis; D010446:Peptide Fragments / Q000134:cerebrospinal fluid*; D011933:Reagent Kits, Diagnostic; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012995:Solubility
chemical_list: C545487:APP protein, human; D016564:Amyloid beta-Protein Precursor; D015415:Biomarkers; D010446:Peptide Fragments; D011933:Reagent Kits, Diagnostic
keywords: Alzheimer's disease; CSF; method validation; soluble APP; standard operating procedures