Broad Approach Required for Histoplasmosis Diagnosis

An immunoassay has been used to improve the diagnosis of histoplasmosis, which is often diagnosed by a combining antigen and antibody testing, as well as culture and pathology.

The sensitivity of the MVista Histoplasma antigen enzyme immunoassay (EIA) has been evaluated in disseminated histoplasmosis in patients with Acquired Immunodeficiency Syndrome (AIDS) and in the “epidemic” form of acute pneumonia.

Scientist at Indiana University (Indianapolis, IN, USA) collected serum and urine samples from 218 patients with histoplasmosis; 158 with disseminated disease and 60 with pulmonary infection, and 229 controls. The patients evaluated came from eight medical centers during the period from November 2004 through December 2007, and they were tested for Histoplasma and/or Blastomyces antigen at a commercial laboratory. The MVista Histoplasma antigen EIA was modified to permit quantification below the level of 0.6 ng/mL by incorporating 0.2 ng/mL and 0.4 ng/mL calibrators and removing those of ≥19 ng/mL. Serum specimens were treated with 4% EDTA at 104 °C before testing.

In the group with disseminated histoplasmosis, the rate of antigenuria, the presence of the specific antigen in the urine, was 91.8%. Sensitivity for the presence of the specific antigen in the serum, antigenemia, was similar. Culture findings were positive in 74.2% of cases, and similar rates were seen with pathology (76.3%) and antibody testing (75.0%). The sensitivity of the test in pulmonary cases varied, as antigenuria was positive in 83.3% of acute cases, in 87.5% of chronic cases, but in only 30.4% of subacute cases. Conversely, antibody results were positive in 66.7%, 95.1%, and 83.3% of those three categories, respectively. The control group included 30 subjects with blastomycosis, and the histoplasmosis tests were 90% cross-reactive in this group. However, the histoplasmosis antigen-enzyme immunoassay was 99% specific when tested in healthy subjects and those with nonfungal infections.

MVista Histoplasma antigen quantative sandwich EIA is a product of MiraVista Diagnostics (Indianapolis, IN, USA) where the laboratory analysis was carried out. Chadi A. Hage, MD, the senior author of the study, and his colleagues concluded that their study supports a broad approach, using antigen testing of urine and serum samples, antibody testing, culture, and pathology for diagnosis of disseminated or pulmonary histoplasmosis. The study was published online on August 2, 2011, in the journal Clinical Infectious Diseases.

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Indiana University
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