Calcofluor white stain for the detection of Pneumocystis carinii in transbronchial lung biopsy specimens: a study of 68 cases.

Calcofluor white (CFW), a chemofluorescent agent, has proven effective in the recognition of Pneumocystis carinii cysts in respiratory fluids and secretions. However, its usefulness in the recognition of P. carinii cysts in tissue preparations has not been established. We studied 68 formalin-fixed, paraffin-embedded, transbronchial tissue biopsy specimens from individuals seropositive for the human immunodeficiency virus and stained them with the CFW stain and the conventional Gomori methenamine silver (GMS) stain to determine the concordance rate of the two stains. CFW-positive specimens showed light peripheral staining and a unique double parenthesis-like structure near the center of the cysts. Thirty-six (52.9%) of the 68 specimens were CFW and GMS positive, whereas 27 (39.7%) of the specimens were negative by both techniques, yielding a concordance rate of 92.6%. Five (7.4%) of the 68 specimens showed disparate results, and, of these, four (5.9%) were CFW positive and GMS negative, whereas one (1.5%) was CFW negative and GMS positive. We conclude that the CFW stain is suitable and useful for the demonstration of P. carinii cysts in tissue preparations.