Comparison of three commercial cryptococcal latex kits for detection of cryptococcal antigen

Three commercial latex kits, IBL, MYCO-Immune, and IMMY, for the detection of cryptococcal antigen were compared in regard to sensitivity, specificity, and height of antigen titers. A total of 218 cerebrospinal fluid and 79 serum specimens from 239 patients were included. Twenty-two patients had culture-proven disseminated cryptococcosis. Both the IBL and MYCO-Immune kits had sensitivities of 100%, and the IMMY kit had sensitivities of 82.6 and 45.4% in CSF and serum specimens, respectively. There was one false-positive reaction in serum with the MYCO-Immune kit and one false-negative reaction on screen only with all three kits. Rheumatoid factor-containing sera were used to check the agglutination titers between matching anti-cryptococcal globulin reagents and normal globulin reagents. The finding that agglutination titer with anti-cryptococcal globulin reagents was fourfold higher than with normal globulin reagents in the MYCO-Immune kit is considered to be a cause for a false-positive reaction in serum.