Role of cytology and polymerase chain reaction based detection of Pneumocystis jirovecii infection in bronchoalveolar lavage fluid

Abstract

Objective: To study the role of cytology and polymerase chain reaction (PCR) for the detection of Pneumocystis carinii pneumonia (PCP) in bronchoalveolar lavage fluid (BALF). Study Design: In a prospective observational study, a BALF pellet from 55 patients (35 immunosuppressed patients clinically suspicious for PCP and 20 immunocompetent individuals not suspicious for PCP) were subjected to cytology examination as well as PCR for PCP using the major surface glycoprotein gene. Additionally, DNA was extracted from destained cytology slide scrapings from 5 cases each positive for PCR and negative for PCP on BALF, respectively, and was further subjected to PCR. Results: Of 35 immunosuppressed patients, 2 were positive on microscopy for PCP, while 5 (including 2 microscopy positive) were positive by PCR from BALF. Four of the 5 positive cases showed predominantly alveolar macrophages, while one showed 40% alveolar macrophages, 30% lymphocytes and 20% neutrophils upon cellular analysis of BALF. One case had coinfection with Cryptococcus. Destained smear scrapings of PCR-positive slides (n=5) were all successfully amplified for PCP major surface glycoprotein PCR after DNA extraction, while control slides (n=5) did not show amplification. Conclusion: BALF is considered the sample of choice for the diagnosis of PCP. In our study, cases with PCP showed mainly alveolar macrophages on BALF examination by cytology and no or mild inflammatory cells. Thus, inflammatory cell population found on cytology may provide direction for PCR. Two-step screening of BALF using cytology followed by PCR from slides is possible and may overcome the limitations of BALF cytology alone for the diagnosis of PCP.