Diagnostic accuracy of ELISA and xMAP technology for analysis of amyloid β42 and tau proteins

Abstract

Background: Cerebrospinal fluid (CSF) concentrations of amyloid β42 (Aβ42) 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 Aβ42, 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 Aβ42, t-tau, and p-tau in CSF, however, differentiation of clinical groups is equivalent when either xMAP technology or conventional ELISA is used. © 2007 American Association for Clinical Chemistry.