New Antigen-Based Tests For Invasive Fungal Disease

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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.

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.

Medline abstract (Free)