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Diagnostic Accuracy of ELISA and xMAP Technology for Analysis of Amyloid ß₄₂ and Tau Proteins

Department of¹ Neurology, ² Alzheimer Centre Nijmegen, ³ Laboratory of Pediatrics and Neurology, and ⁴ Department of Geriatric Medicine, Radboud University Nijmegen Medical Centre, The Netherlands.

^aAddress correspondence to this author at: Department of Neurology, 830 LKN, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands. Fax 31-24-3668754; e-mail m.verbeek{at}cukz.umcn.nl.

Background: Cerebrospinal fluid (CSF) concentrations of amyloid ß₄₂ (Aß₄₂) peptides and tau proteins may serve as biomarkers for Alzheimer disease (AD). Recently, the xMAP technology has been introduced as an alternative to ELISA for measurement of these markers.

Methods: We used xMAP assays and ELISA to analyze CSF concentrations of Aß₄₂, total tau (t-tau), and tau phosphorylated at threonine 181 (p-tau₁₈₁) in samples from 69 patients with Alzheimer disease, 26 patients with vascular dementia, and 55 controls without neurological disorders.

Results: High CV values (>28%) for the ratio of xMAP:ELISA were observed for each biomarker, indicating that a constant correction factor cannot be applied to recalculate xMAP results into ELISA results. When a combination of CSF markers was used, the sensitivity, specificity, and area under the ROC curves for xMAP assays and ELISAs were not significantly different in differentiating AD patients from vascular dementia patients and controls.

Conclusions: A constant conversion factor cannot be used successfully to recalculate results obtained with xMAP assays to those from the ELISAs. With the use of analysis of a combination of Aß₄₂, t-tau, and p-tau in CSF, however, differentiation of clinical groups is equivalent when either xMAP technology or conventional ELISA is used.

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