PURPOSE: For the diagnosis of tuberculous pleural effusion, polymerase chain reaction (PCR) of pleural effusion specimens has shown very low sensitivity, which might be due to the small number of bacilli in the samples. The purpose of this investigation is to determine whether the sensitivity of PCR testing can be improved when increasing the amount of pleural effusion specimens.
METHODS: For one year, we prospectively analyzed pleural effusion specimens obtained from 53 patients for whom the exclusion of the possibility of tuberculous pleural effusion was necessary. We performed M. tuberculosis PCR testing using the Cobas Amplicor MTB test (Roche Diagnostic Systems) with three different amounts (10ml, 25ml, and 50ml) of pleural effusion specimen in each patient. Pleural tuberculosis was defined as having one of the following: culture-positive pleural fluid sample, histopathologic finding consistent with tuberculosis on pleural biopsy, culture-positive sputum specimen, and/or positive response to antituberculosis medication without other possible causes of pleural effusion.
RESULTS: Of the 53 patients, 26 received the diagnosis of pleural tuberculosis. The sensitivities of AFB smearing of pleural effusion specimen, M. tuberculosis culture of pleural effusion specimen, pleural biopsy, and measurement of ADA were 3.8%, 15.4%, 84.6%, and 88.5%, respectively. The results of PCR testing were positive for 3 (11.5%), 4 (15.4%), and 3 (11.5%) of the 26 patients when using 10ml, 25ml, and 50ml of pleural effusion specimens, respectively. These results did not show a statistically significant difference in the sensitivity of PCR testing when increasing the amount of pleural effusion samples (p >0.05, symmetry exact test).
CONCLUSION: For specimens such as pleural effusion, in which the bacillary load is very low, the clinical utility of PCR testing seems highly limited. An increased amount of pleural effusion sample does not improve the sensitivity of PCR testing.
CLINICAL IMPLICATIONS: PCR testing of pleural effusion specimens has a low sensitivity and thus does not seem to be useful in excluding pleural tuberculosis. Therefore, it cannot replace the conventional diagnostic methods including culture techniques and histopathologic examinations.
DISCLOSURE: Jin Wook Moon, None.