High detection rates of cryptococcal antigen in pulmonary cryptococcosis by Eiken Latex Agglutination test with pronase pretreatment

Two different kits for the detection of serum cryptococcal antigen in patients with pulmonary cryptococcosis were evaluated. The Eiken test (the Eiken Co., Tokyo), which uses pronase for pretreatment of serum, was compared with the Crypto-LA test (International Biological Laboratories, Cranbury, NJ), which did not use pronase prior to testing. Cryptococcal antigen was detected in 21 of 23 patients (91%) with the Eiken test and in only 10 of 23 patients (43%) with the Crypto-LA test (p<0.01 by Mcnemar test). However, the sensitivity of two tests was identical without use of pronase, as both tests could detect as little as 10⁴ cells/ml ofCryptococcus neoformans and 10 ng/ml of capsular polysaccharide ofC. neoformans. In those serum specimens for which both tests were positive, titers were much higher for the Eiken test, but there was a statistically significant correlation between the two tests (coefficient correlation 0.79,p<0.01). Cryptococcal antigen titer levels measured by the Eiken test correlated well with clinical courses. There was one false-positive reaction among 82 sera of non-cryptococcal patients. Pronase enhanced the sensitivity of the Eiken test, which appeared to be useful in patients with pulmonary cryptococcal disease, and its use may prevent unneeded lung biopsies.