Optimization of the cutoff value for the Aspergillus double-sandwich enzyme immunoassay.
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 > or = 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.
Maertens
Johan A
JA
Department of Hematology, Universitaire Ziekenhuizen, Catholic University Leuven, Leuven, Belgium. johan.maertens@uz.kuleuven.ac.be
Klont
Rocus
R
Masson
Christine
C
Theunissen
Koen
K
Meersseman
Wouter
W
Lagrou
Katrien
K
Heinen
Christine
C
Crépin
Brigitte
B
Van Eldere
Johan
J
Tabouret
Marc
M
Donnelly
J Peter
JP
Verweij
Paul E
PE
D000293:Adolescent; D000328:Adult; D000368:Aged; D001228:Aspergillosis / Q000097:blood / Q000175:diagnosis* / Q000382:microbiology; D001230:Aspergillus / Q000302:isolation & purification*; D005260:Female; D005690:Galactose / Q000031:analogs & derivatives; D006801:Humans; D007124:Immunoenzyme Techniques / Q000379:methods* / Q000592:standards; D008297:Male; D008351:Mannans / Q000032:analysis; D008875:Middle Aged; D009503:Neutropenia / Q000276:immunology / Q000382:microbiology; D012372:ROC Curve; D012189:Retrospective Studies; D012680:Sensitivity and Specificity
D008351:Mannans; C012990:galactomannan; D005690:Galactose