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Assays for Invasive Fungal Disease

Two new antigen-based tests show promise and could prove useful for immunocompromised patients.

Early diagnosis and therapy is critical to the management of patients with invasive fungal disease (IFD). Although diagnosis has been based on culture or microscopy, antigen-based assays to detect (13)-β-D-glucan (BG) and Aspergillus galactomannan recently became available. Both rely on identification of polysaccharides associated with the cell wall of fungal pathogens. Now, two research groups have examined the performance and usefulness of these assays in patients at risk for IFD.

Koo and colleagues retrospectively reviewed the results of 1308 serum BG assays performed for 871 patients. For patients tested more than once, the results of the first BG test were used. A BG level 80 pg/mL had a sensitivity of 64% and a specificity of 84% for a diagnosis of IFD within 1 week. Sensitivity was 71% and specificity was 81% for such a diagnosis by the end of hospitalization. Albumin, intravenous immunoglobulin, and hemodialysis independently increased BG levels. When patients with these factors were excluded from analysis, the specificity of the test increased slightly, but the sensitivity remained unchanged.

Maertens and colleagues examined the use of the Platelia Aspergillus galactomannan assay on bronchoalveolar lavage (BAL) fluid from patients hospitalized for hematologic disorders. (One of the authors has received support from the assay maker.) Among 99 BAL samples, the mean optical density for the assay was 4.3 for 58 patients with proven or probable invasive pulmonary aspergillosis (IPA) compared with 0.6 for 41 controls without this diagnosis. At an optical density 1.0, sensitivity was 91% and specificity was 88% for diagnosing IPA. For culture or microscopy, the sensitivity was only 74%.

Comment: These reports indicate the value of newer, antigen-based techniques for diagnosing IFD. Because neither assay depends on host immune response, both are useful for immunocompromised patients. Although caveats remain regarding their interpretation, these tests are important additions to our armamentarium.

— Neil M. Ampel, MD

Published in Journal Watch Infectious Diseases November 18, 2009

Citation(s):

Maertens J et al. Bronchoalveolar lavage fluid galactomannan for the diagnosis of invasive pulmonary aspergillosis in patients with hematologic diseases. Clin Infect Dis 2009 Dec 1; 49:1688.

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• Medline abstract (Free)

Koo S et al. Diagnostic performance of the (13)-β-D-glucan assay for invasive fungal disease. Clin Infect Dis 2009 Dec 1; 49:1650.

• Original article (Subscription may be required)
• Medline abstract (Free)

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