Histoplasmosis: Laboratory Diagnosis

Abstract

The diagnosis of histoplasmosis is based on clinical, imaging, and laboratory evidence of the disease. The gold standards of laboratory diagnosis are the presence of the fungus in the pathological examination of tissues and its isolation (direct microscopy, histopathology, cytopathology) in mycological culture (4–6 weeks required) by clinical specimens. The antibody test, sometimes negative in immunocompromised patients, must be performed at least four weeks after acute infection to be positive. The antibody test is most useful in subacute and chronic forms of histoplasmosis. The antigen test is the most common method for establishing the diagnosis of acute pulmonary histoplasmosis or progressive disseminated histoplasmosis. The antigen test in urine or serum has good sensitivity, better in bronchoalveolar lavage fluid. There are skin sensitivity tests with low sensitivity that are used only for epidemiologic studies and are not recommended for diagnosis. Molecular diagnosis has improved the sensitivity of clinical specimens. Laboratory PCR assays with different molecular targets have been developed. Currently, the main procedure for molecular diagnosis of histoplasmosis is the application of a rapid DNA probe on a fungus isolated from a culture. This chapter summarizes the currently available tools for the laboratory diagnosis of histoplasmosis, focusing on the complexity of the assays and their performance in different clinical contexts.