The use of an indirect fluorescent antibody test for detecting Pneumocystis carinii

Pneumocystis carinii pneumonia is a major cause of morbidity and mortality in immunocompromised patients. An indirect fluorescent antibody (IFA) test has been developed using monoclonal antibodies specific for antigens on the surface of P carinii. We tested the sensitivity and specificity of this IFA test for detecting P carinii in respiratory specimens of immunocompromised patients with pulmonary symptoms undergoing bronchoscopy. Both the bronchial wash and bronchoalveolar lavage specimens of patients with and without P carinii pneumonia were studied. The bronchoalveolar lavage and bronchial wash specimens were examined using modified Wright-Giemsa and methenamine silver stains. In addition, aliquots of the specimen were fixed and stained with IFA and read with a fluorescent microscope. Fifty-nine patients were found to have P carinii organisms. The bronchial wash specimen has been shown to be less sensitive than the bronchoalveolar lavage specimen for detecting the presence of P carinii. In the bronchial wash specimen from these 59 patients, only 60% had positive modified Wright-Giemsa stains, and 70% had positive methenamine silver stains. The IFA stain was positive in 93% of the specimens tested (significantly higher than the other two stains). There was only one false-positive IFA test result among the 54 patients tested with negative results. We found the IFA stain to be superior to conventional stains when examining less-than-adequate specimens, such as those from bronchial washes.