Purpose of review: To define the most appropriate studies for making a diagnosis of histoplasmosis in immunosuppressed patients.
Recent findings: As is true of all fungal infections in immunosuppressed patients, heightened awareness of the epidemiology and clinical manifestations of histoplasmosis is essential in making an early diagnosis. Increasingly, Histoplasma antigen detection is used to help establish a diagnosis of histoplasmosis. Most of the reported data are on patients with AIDS, but limited data suggest the usefulness of this assay in other immunosuppressed patients as well. False positive reactions occur with other fungal infections, especially blastomycosis, and patients who have histoplasmosis may have a false positive serum Aspergillus galactomannan assay. The identification of the yeast phase of Histoplasma capsulatum in tissue biopsy samples and, uncommonly, in circulating blood phagocytes is also helpful in establishing a diagnosis quickly. PCR techniques have yet to prove useful for the rapid diagnosis of histoplasmosis, and serology is often negative in immunosuppressed patients. Culture remains definitive and should always be performed to confirm the results of the rapid diagnostic studies.
Summary: Rapid techniques, mostly antigen detection in serum and urine and histopathological identification of Histoplasma capsulatum in tissues, are the most important rapid diagnostic tests for histoplasmosis in immunosuppressed patients.