Thus, the major prognostic determinant is often the degree of pulmonary function remaining when therapy is instituted. The diagnosis of histoplasmosis depends on the isolation of the H. capsulatum organism in culture. The lysis centrifugation blood-culturing technique is the most sensitive method for detecting H. capsulatum organisms in the blood. Immunologic techniques are not as reliable as they are in other infectious diseases. Intradermal skin testing with histoplasmin is a useful epidemiologic tool.
Serologic tests can be more useful than the histoplasmin skin test.
The mycelial-phase titer commonly rises about 1 month after acute infection and disappears within a few weeks or months. The yeast-phase titer begins to rise somewhat later and persists for many years. Demonstration of complement-fixing antibodies in the CSF can be quite useful in diagnosing meningitis caused by H. capsulatum.38 Immunodiffusion and counterimmunoelectrophoresis have been used to detect the M and H precipitin bands. Precipitating antibodies to the M antigen appear early in the course of histoplasmosis and persist for months to years. Disseminated histoplasmosis can be diagnosed rapidly by the detection of H. capsulatum polysaccharide antigens in serum and urine, and the performance of serial studies to measure these antigens can be both a useful guide to treatment and a warning of impending relapse.