Journal Article

Optimization of the Cutoff Value for the Aspergillus Double-Sandwich Enzyme Immunoassay

Lagrou, Katrien, Donnelly, J. Peter, Maertens, Johan A., Verweij, Paul E., Heinen, Christine, Crépin, Brigitte, Meersseman, Wouter, Theunissen, Koen, Tabouret, Marc, Masson, Christine, Klont, Rocus, Eldere, Johan Van

2007

Overview

Background.Many health care centers worldwide use the Platelia Aspergillus enzyme immunoassay (PA-EIA; Bio-Rad Laboratories) for diagnosis of invasive aspergillosis (IA). A cutoff optical density (OD) index of 1.5 was originally recommended by the manufacturer, but in practice, most institutions use lower cutoff values. Moreover, a cutoff OD index of 0.5 was recently approved in the United States. In the present study, we set out to optimize the cutoff level by performing a retrospective analysis of PA-EIA values for samples that had been obtained prospectively from adult patients at risk for IA at 2 European health care centers. Methods.In total, 239 treatment episodes were included of which there were 19 episodes of proven IA and 19 episodes of probable IA. Per-episode and per-test analyses and receiver operating characteristic curves were used to determine the optimal cutoff value. Results.In the per-episode analysis, lowering the cutoff OD index for positivity from 1.5 to 0.5 increased the overall sensitivity by 21% (from 76.3% to 97.4%) but decreased the overall specificity by 7% (from 97.5% to 90.5%). Requiring 2 consecutive samples with an OD index ⩾0.5 resulted in the highest test accuracy, with an improved positive predictive value. At a cutoff OD index of 0.5, the antigen test result was positive during the week before conventional diagnosis in 65% of cases and during the week of diagnosis in 79.5% of cases. Conclusions.A cutoff OD index of 0.5—identical to the approved cutoff in the United States—improves the overall performance of the PA-EIA for adult hematology patients.

• Publisher: The University of Chicago Press,University of Chicago Press,Oxford University Press
• Subject: Adolescent / Adult / Adults / Aged / Antigens / Articles and Commentaries / Aspergillosis / Aspergillosis - blood / Aspergillosis - diagnosis / Aspergillosis - microbiology / Aspergillus / Aspergillus - isolation & purification / Biological and medical sciences / Clinical outcomes / Control groups / Diagnostic indices / Enzymes / Female / Fungal infections / Fungi / Health care / Human mycoses / Humans / Immunoassay / Immunoenzyme techniques / Immunoenzyme Techniques - methods / Immunoenzyme Techniques - standards / Infectious diseases / Male / Mannans - analysis / Medical diagnosis / Medical sciences / Middle Aged / Miscellaneous mycoses / Mycoses / Neutropenia - immunology / Neutropenia - microbiology / Nonnative species / Optical density / Patients / Retrospective Studies / ROC Curve / Sensitivity and Specificity / Test ranges