Histoplasmosis: To Skin Test or Not to Skin Test?

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Abstract
A total of 187 persons received a single intradermal skin test employing a 1:100 dilution of commercially-available histoplasmin. The group was bled immediately prior to skin testing, at 8 weekly intervals thereafter, and then every 2 weeks through the 3rd month. The collodion agglutination and yeast phase complement-fixation tests, routinely employed in this laboratory, were used. For comparison, histoplasmin complement-fixation and latex agglutination tests were performed. Ninety (48.1%) individuals exhibited a positive histoplasmin skin test. No significant antibody changes were detected in the sera of the 187 subjects when measured by the yeast phase complement-fixation, collodion agglutination or latex agglutination tests. Similarly with histoplasmin as antigen, none of 97 skin-test negative individuals developed significant increases in complement-fixation titers, but 24 (26.7%) of 90 skin-test positive persons developed significant 4-fold or greater titer increases with peak titers of 1:10 to 1:160 by the 3rd to 4th weeks. Differences in results obtained after a single histoplasmin skin test have varied from laboratory to laboratory. Variables such as skin-test antigen, type of sero-logic test and antigens employed therein, and size of group studied could account for differences in results. It is therefore incubent on each labatory performing such tests to evaluate periodically these tests in terms of response to the skin-test antigen employed.