Evaluation of an enzyme-linked immunosorbent assay that uses ferrous metal beads for determination of antihistoplasmal immunoglobulins G and M

A rapid enzyme-linked immunosorbent assay (ELISA) for the detection of human class-specific antibodies to Histoplasma capsulatum (histoplasmal immunoglobulin M [HIgM] and histoplasmal IgG [HIgG]) was developed by using antigen adsorbed onto polycarbonate-coated ferrous beads. In the ELISA method all the reagents used were commercially available. In 135 specimens from patients with confirmed histoplasmosis, sensitivities were 76% for complement fixation (CF), 53% for immunodiffusion (ID), and 64% for the ELISA for HIgM and HIgG combined. The ELISA detected histoplasmal antibody in 36% of the specimens with negative antibody titers by CF and 46% of the specimens with negative antibody titers by ID. The ELISA detected histoplasmal antibody in 27% of specimens that were negative by both CF and ID. When limited to specimens collected within 4 months of the onset of histoplasmosis symptoms, sensitivities were 82% for CF, 63% for ID, and 86% for ELISA for HIgG and HIgM combined. Within this group, ELISA detected histoplasmal antibody in 90% of the specimens that were negative by CF, 76% that were negative by ID, and 100% that were negative by both CF and ID. The specificity of the ELISA could not be fully addressed since sera from patients with other fungal infections were not available.