The morphologic identification of Pneumocystis carinii.

The diagnosis of Pneumocystis carinii infection is dependent upon morphologic identification of the organism, making the staining properties of P. carinii important to the cytologist engaged in clinical service or research. Several special stains specific for P. carinii are described; in addition, the staining characteristics of the organism in Papanicolaou and in hematoxylin and eosin stains are described. The successful identification of P. carinii with the latter two stains has not been reported previously. Because these stains are often used on lung preparations, it may be possible to identify P. carinii when using these latter two techniques; however, for optimal results, we feel that it is essential to utilize one or more of the special stains discussed herein.