Histoplasmosis-Associated Cross-Reactivity in the BioRad Platelia Aspergillus Enzyme Immunoassay

Abstract

We observed false-positive results in the Platelia Aspergillus enzyme-linked immunoassay (EIA) for specimens from patients with histoplasmosis and mice with experimental infection. Platelia Aspergillus EIA-positive specimens were negative in the second-generation Histoplasma antigen EIA. Care must be taken to exclude histoplasmosis for patients with positive Platelia Aspergillus EIA results.The Platelia Aspergillus enzyme-linked immunoassay (EIA) detects a galactomannan antigen produced by several molds (5). However, studies to date have not included Histoplasma capsulatum. We recently observed false-positive results in the Platelia Aspergillus EIA for specimens from six patients with culture-proven histoplasmosis, as have others (4). Based upon these observations (Table 1), we conducted a laboratory-based study of specimens submitted for Platelia Aspergillus EIA or Histoplasma antigen testing and evaluated cross-reactivity in experimental models of histoplasmosis and aspergillosis.(Part of this work was presented at the 46th Interscience Conference on Antimicrobial Agents and Chemotherapy, 27 to 30 September 2006.)Residual serum and bronchoalveolar lavage (BAL) fluid specimens that were submitted to MiraVista Diagnostics for Histoplasma antigen testing or Platelia Aspergillus EIA and were positive were retested the following day in the other EIA. The second-generation Histoplasma antigen EIA (MiraVista Diagnostics, Indianapolis, IN) uses polyclonal antibodies to H. capsulatum and has been described elsewhere (6). Results of Ն1 unit were regarded as positive. The Platelia Aspergillus EIA (Bio-Rad Laboratories, Redmond, WA) uses monoclonal antibodies produced against Aspergillus fumigatus. Specimens were pretreated with EDTA for the Platelia Aspergillus EIA and boiled in accordance with the manufacturer's specifications. Results with a galactomannan index (GMI) of 0.5 or greater were reported as positive. Note that the Platelia Aspergillus EIA is not FDA cleared for specimens other than serum.Twenty-three of 48 serum specimens positive for antigen in the second-generation Histoplasma antigen EIA were positive in the Platelia Aspergillus EIA (Fig. 1). Positive results were more frequent for specimens giving levels of 40 units or higher in the Histoplasma antigen EIA (12/17 [70.6%]) than for those giving levels below 40 units (11/31 [35.5%]) (P ϭ 0.043 by chi-square test). As controls, 12 serum specimens that were negative in the Histoplasma antigen EIA were tested in the Platelia Aspergillus EIA, and all were negative. Seven of 11 (63.6%) BAL fluid specimens that were positive in the Histoplasma antigen EIA were positive in the Platelia Aspergillus EIA. Results for the Histoplasma antigen EIA ranged from 2.2 to 61.7 units for the BAL fluid specimens that were positive in the Platelia Aspergillus EIA, compared to 4.2 to 21.2 units for those that were negative. Ten control BAL fluid specimens that were negative in the Histoplasma antigen EIA were negative in the Platelia Aspergillus EIA.Twenty serum specimens that w...

Cross-Reactivity in the Histoplasma Antigen Enzyme Immunoassay Caused by Sporotrichosis

“…Four isolates of S. schenckii were incubated at 37°C for 7 days in Histoplasma macrophage medium (12), and culture supernatants were tested in the Platelia Aspergillus EIA and the Histoplasma antigen EIA. Aspergillus galactomannan was detected in the culture supernatants from all four isolates, and Histoplasma antigen was detected in one (Table 1), suggesting weak cross-reactivity, as observed with Aspergillus galactomannan (11).…”

Cross-Reactivity of Fusarium spp. in the Aspergillus Galactomannan Enzyme-Linked Immunosorbent Assay

“…Cross-reactivity with antigens released by a large number of fungi has been reported in the literature (1,3,4,8,20,21). Test specificity with exoantigens of Fusarium cultures is controversial (1,6,16).…”

“…The epitope detected by the EB-A2 monoclonal antibody employed in the EIA is not exclusively present in Aspergillus species. This epitope is contained also in antigens of other molds, including Penicillium, Paecilomyces, Trichothecium, Geotrichum, and Myceliophthora, of dimorphic fungi, such as Blastomyces dermatitidis and Histoplasma capsulatum, and also of yeasts (1,3,4,8,20,21). Cross-reactivity of Fusarium spp.…”

Invasive Fungal Infections in Patients with Acute Leukemia and Hematopoietic Stem Cell Transplant Recipients

“…False positivity of GM assay was also described in case of infection with Penicillium spp. [78] and Histoplasma capsulatum [79] because these microorganisms share cross reactive antigens. GM can also be detected in other body fluids during IA infection involving those fluids or adjacent tissues, including urine, CSF and bronchoalveolar lavage (BAL) [80][81][82]; however, clinical utility of the assay obtained from other sources than serum is under clinical investigation.…”