Journal Article

Optimization of the Cutoff Value for the <i>Aspergillus</i> Double-Sandwich Enzyme Immunoassay

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

in Clinical Infectious Diseases

Published on behalf of Infectious Diseases Society of America

Volume 44, issue 10, pages 1329-1336
Published in print May 2007 | ISSN: 1058-4838
Published online May 2007 | e-ISSN: 1537-6591 | DOI:
Optimization of the Cutoff Value for the Aspergillus Double-Sandwich Enzyme Immunoassay

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  • Infectious Diseases
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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.

Journal Article.  4179 words.  Illustrated.

Subjects: Infectious Diseases ; Immunology ; Public Health and Epidemiology ; Microbiology

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