CVI Accepts, published online ahead of print on 3 October 2007

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Clin. Vaccine Immunol. doi:10.1128/CVI.00071-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Improvement in the detection of Histoplasma antigen by a quantitative enzyme immunoassay

Patricia A. Connolly^*, Michelle M. Durkin, Ann M. LeMonte, Emily J. Hackett, and L. Joseph Wheat

MiraVista Diagnostics and Mirabella Technologies, Indianapolis, Indiana

^* To whom correspondence should be addressed. Email: pconnolly{at}miravistalabs.com.

Background: The second generation Histoplasma antigen immunoassay is semi-quantitative, expressing results as a comparison to a negative control which requires repeat testing of the prior with the current specimen to accurately determine change in antigen. Reporting results in this manner is often confusing to the ordering physician and laboratory. Development of a quantitative assay could improve accuracy, reduce interassay variability and eliminate the need to test the prior sample with the current in the same assay.

Methods: Calibrators with known concentrations of Histoplasma antigen were used to quantitate antigen in specimens from patients with histoplasmosis and controls. Samples from cases of disseminated histoplasmosis or other mycoses and controls were tested to evaluate the performance characteristics of the quantitative assay. Paired specimens were evaluated to determine if quantitation eliminated the need to test the current and prior specimens in the same assay to assess change in antigen.

Results: Sensitivity in samples from patients with AIDS and disseminated histoplasmosis was 100% in urine and 91% in serum. Cross reactions occurred in 70% of other endemic mycoses but not aspergillosis. Specificity was 99% in controls with community acquired pneumonia, medical conditions in which histoplasmosis was excluded, or healthy subjects. Change in antigen level categorized as increase, no change or decrease based on antigen units determined in the same assay agreed closely with the category of change in ng/mL determined from testing current and prior specimens in different assays.

Conclusion: Sensitivity, specificity and interassay precision are excellent in the new 3^rd generation quantitative Histoplasma antigen immunoassay.

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