Usefulness of polymerase chain reaction method in the early diagnosis of Pneumocystis carinii pneumonia

We evaluated the sensitivity and specificity of polymerase chain reaction (PCR) method in the detection of Pneumocystis carinii, and compared its clinical usefulness with that of a previous method, toluidine blue-O (TBO) staining in diagnosis of P. carinii pneumonia (PCP) using clinical samples such as sputum and bronchoalveolar lavage fluid (BALF). Using P. carinii obtained from BALF of the infected rats, we showed that PCR showed 100 fold more sensitivity than TBO staining as indicated by the comparison of their detection limits (78 cysts/ml vs 7800 cysts/ml). In addition, the detection using PCR in this study was specific for P. carinii because all other pathogens examined were not positive. In the clinical study we analyzed 44 patients including 10 with definite PCP, 8 with portable PCP and 26 with other diagnosis. In the sputum, the sensitivity and specificity were 100% and 95%, respectively, in PCR, while 13% and 100% in TBO staining. These results revealed that PCR was much superior to TBO staining in sensitivity especially when the sputum was used as samples, and suggested that examination of the sputum by PCR was clinically very useful in early diagnosis of P. carinii pneumonia.