Significance of serum antibodies to Histoplasma capsulatum in endemic areas.

To evaluate the specificity of serologic tests for histoplasmosis in an endemic area, we studied sera from 104 consecutive healthy blood donors, testing for antibodies to either histoplasmin or Histoplasma yeast antigen, using complement fixation (CF), radioimmunoassay (RIA), and radial immunodiffusion (ID). Twenty-five subjects (24%) had CF antibody titers of 1:8 or 1:16 to one or both antigens; none had titers above 1:16. Nine subjects (9%) had RIA antibody titers of 1:8 or higher. No titers above 1:8 were found using the yeast antigen; five subjects had titers of greater than 1:16 to histoplasmin using RIA. No precipitin bands were found in any of these subjects. The results of four previous studies in endemic populations yielded similar or lower incidences of positive tests. CF antibody titers to either antigen, RIA antibody titers to yeast antigen of 1:32 or greater, or precipitin bands are rare in persons who live where histoplasmosis is endemic.