title: Amyloid-β 42/40 cerebrospinal fluid concentration ratio in the diagnostics of Alzheimer's disease: validation of two novel assays.
abstract: BACKGROUND
  The increasing role of cerebrospinal fluid (CSF) biomarkers in the early diagnosis of Alzheimer's disease (AD) is reflected in recently published diagnostic and/or research criteria. A growing body of evidence suggests better diagnostic performance of the amyloid-β (Aβ)42/40 CSF concentration ratio compared to the Aβ42 concentration alone.
  
  
  OBJECTIVE
  (a) to analytically validate two novel ELISAs capable to measure Aβ1-40 and Aβ1-42 in the CSF, and (b) to compare the diagnostic accuracies of Aβ1-42 and Aβ42/40 ratio.
  
  
  METHODS
  In this study, (a) the novel Aβ1-40 and Aβ1-42 ELISAs (IBL International GmbH, Hamburg, Germany) have been analytically validated, and (b) a clinical study has been performed comparing the diagnostic performance of the CSF Aβ42/40 concentration ratio and the CSF Aβ42 concentration.
  
  
  RESULTS
  In the analytical part of the study, only marginal cross-reactivity (Aβ1-42 versus Aβ1-40) was observed; recoveries were in the range of 85-100% for the samples diluted 1 : 20-1 : 640 (Aβ1-40), and 92-104% for the samples diluted 1 : 20-1 : 320 (Aβ1-42). For Aβ1-40, the intra-assay imprecision was 2.1%, the inter-assay imprecision was 4.4%, and the inter-lot imprecision was 5.4 %. For Aβ1-42, the numbers were 3.1%, 6.2%, and 6.9%, respectively. The goodness of the fit of the average standard curves was >0.99 for both assays, and the imprecision of the optical densities in ten repetitions of the standard curves was ≤5% for all standards. In the clinical part, at the cut off value 691 pg/mL, Aβ1-42 showed sensitivity and specificity of 69.3% and 88.9%, respectively, whereas at the cut off value 0.06, the Aβ42/40 ratio showed significantly improved performance with sensitivity and specificity of 93.3% and 100%, respectively. The area under the ROC curve for Aβ42/40 (0.974) was highly significantly larger compared to Aβ1-42 concentration ROC curve (0.827, p < 0.0001).
  
  
  CONCLUSIONS
  (a) the novel Aβ1-40 and Aβ1-42 ELISA assays characterize with very good analytical performance; (b) we reconfirm that the CSF Aβ42/40 concentration ratio shows significantly better diagnostic performance compared to the CSF Aβ1-42 concentration alone.
authors: Department of Psychiatry and Psychotherapy, Universitätsklinikum Erlangen, and Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany.
authors: Piotr
authors: P
authors: Lewczuk
authors: Department of Psychiatry and Psychotherapy, Universitätsklinikum Erlangen, and Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany.
authors: Natalia
authors: N
authors: Lelental
authors: Department of Psychiatry and Psychotherapy, Universitätsklinikum Erlangen, and Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany.
authors: Philipp
authors: P
authors: Spitzer
authors: Department of Psychiatry and Psychotherapy, Universitätsklinikum Erlangen, and Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany.
authors: Juan Manuel
authors: JM
authors: Maler
authors: Department of Psychiatry and Psychotherapy, Universitätsklinikum Erlangen, and Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany.
authors: Johannes
authors: J
authors: Kornhuber
mesh_terms: D000368:Aged; D000544:Alzheimer Disease / Q000134:cerebrospinal fluid* / Q000175:diagnosis*; D016229:Amyloid beta-Peptides / Q000134:cerebrospinal fluid*; D019540:Area Under Curve; D015415:Biomarkers / Q000134:cerebrospinal fluid; D060825:Cognitive Dysfunction / Q000134:cerebrospinal fluid / Q000175:diagnosis; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010446:Peptide Fragments / Q000134:cerebrospinal fluid*; D012372:ROC Curve; D012680:Sensitivity and Specificity
chemical_list: D016229:Amyloid beta-Peptides; D015415:Biomarkers; D010446:Peptide Fragments; C078592:amyloid beta-protein (1-40); C075222:amyloid beta-protein (1-42)
keywords: A$\beta_{42/40}$ ratio; Alzheimer's disease; amyloid-β; biomarkers; cerebrospinal fluid; validation