Pneumocystis jirovecii immunostain versus Gomori/Grocott methenamine silver stain of bronchoalveolar lavage in cell blocks: an institutional experience.

Introduction: Current approaches to Pneumocystis jirovecii (PCJ) screening on bronchioalveolar lavage samples (BAL) include Gomori/Grocott methenamine silver stain (GMS), toluidine blue O stain, Wright-Giemsa stain, immunofluorescent antibody stain, and polymerase chain reaction. Another method available is PCJ immunohistochemistry stain (PCJ IHC). There are no published series evaluating the efficacy of PCJ IHC in cell block preparation of BAL, we sought to compare GMS versus PCJ IHC at our institution.

Materials And Methods: We performed a retrospective analysis at our institution of all BAL with cell blocks where PCJ IHC and GMS were done simultaneously since March 2015.

Results: 982 BAL samples were identified from 640 patients (median age: 54 years; range: 1-84 years). For 895 cases, GMS and PCJ IHC were performed simultaneously. PCJ was identified in 14 samples, from 13 patients (2.2% of patients) using PCJ IHC. GMS stains were read as positive in only 6 of these 14 cases (42.8%); in two of those cases, PCJ was easily identified on routine Papanicolaou stains. We repeated GMS staining on those 14 cases following before-schedule maintenance in our Ventana Benchmark Autostainer, identifying 12 cases positive. In addition, a significantly higher number of organisms was seen on repeat GMS (median: 58) than the original GMS (median: 8.7). Nevertheless, a statistically significant higher number of organisms was detected by PCJ IHC (median: 474).

Conclusions: PCJ IHC performed in cell block is more sensitive and specific than GMS and is a reliable marker when a low number of PCJ organisms are present.