Detection of cryptococcal antigen. Comparison of two latex agglutination tests

The detection of cryptococcal antigen by means of the agglutination of antibody-coated latex particles is an important aid in the diagnosis of cryptococcosis. A commercially available latex agglutination test (IBL kit) was compared with the latex agglutination test from the Center for Disease Control in regard to sensitivity, specificity, and height of antigen titer. Over a 13-month period, 335 specimens were tested with both kits. There was one false-positive reaction with both kits (0.4%) and one false-negative reaction only with the CDC kit, among 18 patients who had meningitis or disseminated infection due to Cryptococcus neoformans. Sera from patients who had localized pulmonary cryptococcosis showed negative results with both kits. The antigen titers measured by the two kits were the same or within two dilutions in 22 of 26 specimens of cerebrospinal fluid or serum from patients who had proved cryptococcosis. Overall, the IBL kit compared favorably with the CDC kit for the detection of cryptococcal antigen in cerebrospinal fluid or serum.