Received on October 11, 2006
Accepted on February 23, 2007

Proteomics and Protein Markers

Diagnostic Accuracy of ELISA and xMAP Technology for Analysis of Amyloid ₄₂ and Tau Proteins

¹ Departments of Neurology, and Alzheimer Centre Nijmegen; Laboratory of Pediatrics and Neurology, Radboud University Nijmegen Medical Centre, The Netherlands
² Departments of Alzheimer Centre Nijmegen, and Geriatric Medicine, Radboud University Nijmegen Medical Centre, The Netherlands
³ Department of Laboratory of Pediatrics and Neurology, Radboud University Nijmegen Medical Centre, The Netherlands
⁴ Department of Neurology, Radboud University Nijmegen Medical Centre, The Netherlands
⁵ Departments of Neurology, Alzheimer Centre Nijmegen, and Laboratory of Pediatrics and Neurology, Radboud University Nijmegen Medical Centre, The Netherlands

^* To whom correspondence should be addressed. E-mail: m.verbeek{at}cukz.umcn.nl.

Background: Cerebrospinal fluid (CSF) concentrations of amyloid ₄₂ (A₄₂) 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 A₄₂, 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 A₄₂, t-tau, and p-tau in CSF, however, differentiation of clinical groups is equivalent when either xMAP technology or conventional ELISA is used.