Effect of Histoplasmin Skin Testing on Serologic Results.

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Abstract
Repeated positive histoplasmin skin tests in normal medical students caused false positive reactions in the collodion agglutination test (57.1%) and in the complement-fixation test with Histoplasma yeast phase antigen (78.6%) or with histoplasmin as antigen (85.7%). The response was relatively transient in the former 2 tests, and negative titers were usually restored by 21 weeks after the last skin test. However, positive results were noted as late as 21, 25 and 39 wks. in complement-fixation tests employing histoplasmin as antigen. A transient response was observed in complement-fixation studies with cross-reacting yeast phase blastomyces antigens (57.1%), but no sera reacted in the same test with coccidioidin antigen. A single positive skin test and repeated negative skin tests did not alter serologic results. Thus, repeated histoplasmin skin testing of skin-test positive persons may invalidate complement-fixation data for long periods with histoplasmin as antigen, and for much shorter periods with yeast phase histoplasma and blastomyces complement-fixation or histoplasmin collodion agglutination tests.
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