Comparison of Enzyme Immunoassay and Latex Agglutination Test for Detection of Cryptococcal Antigens

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We developed an enzyme immunoassay system (EIA-1) to compare its sensitivity and specificity with those of a commercially available EIA kit (EIA-2) and with a latex agglutination (LA) kit prepared in our laboratory. When antigens were diluted with buffer, the minimal detectable concentration of polysaccharide antigens from Cryptococcus neoformans serotypes A and B was 0.10ng/ml and 0.05ng/ml, respectively. The EIA-1 was found to be 32-fold more sensitive than EIA-2, and 64-fold (for serotype A) and 256-fold (for serotype B) more sensitive than the LA test. Cross-reactivity with Candida albicans and Aspergillus fumigatus antigens was not observed with either EIA, nor did rheumatoid factor give a false-positive reaction. However, when capsular polysaccharides were diluted with human serum, the sensitivity of both EIAs decreased. With sera from patients, although sensitivity of the EIA-2 test was similar to that of the LA test, EIA-1 exhibited lower antigen titers than did the other two tests. It was suggested that EIA using monoclonal antibodies is affected by serum condition. Taken together, because of its sensitivity, specificity, ease of performance, reproducibility and rapidity, except for a pretreatment procedure for rheumatoid factor, the LA test would be the most useful for serodiagnosis of cryptococcosis.