Affiliations: Department of Psychiatry and Psychotherapy, Universitätsklinikum Erlangen, and Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany
Correspondence:
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Correspondence to: Prof. Dr. med. Piotr Lewczuk, Lab for Clinical Neurochemistry and Neurochemical Dementia Diagnostics, Department of Psychiatry and Psychotherapy, Schwabachanlage 6, 91054 Erlangen, Germany. Tel.: +49 9131 85 34324; Fax: +49 9131 85 34 238; E-mail: Piotr.Lewczuk@uk-erlangen.de.
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.
