Clinical Utility of Polymerase Chain Reaction for Diagnosis of Smear-negative Pleural Tuberculosis

BackgroundPolymerase chain reaction (PCR) is a molecular biology technique which can detect Mycobacterium tuberculosis (TB) genome in pleural fluid; however, the results are variable.MethodsTwo hundred and twelve pleural fluid specimens suspected to be possibly associated with tuberculosis with negative acid-fast smears were sent to our laboratory to test for the presence of M. tuberculosis DNA using nested PCR, the target for the amplification being a segment of IS6110 in the genome of M. tuberculosis. The final diagnosis of TB pleurisy was based on combining clinical judgment with radiologic findings, microbiologic tests, and the histopathologic findings. Forty-nine patients were excluded due to incomplete or inconsistent clinical information.ResultsOf 163 patients enrolled, PCR was positive in 23 (43.4%) of 53 patients with TB pleurisy and 5 (4.5%) of 110 patients with non-TB pleurisy, with a sensitivity and specificity of 43.4% and 95.5%, respectively. Positive culture of pleural fluid was found in 15 (28.3%) of the TB pleurisy group and none in the non-TB group. Fifteen (55.6%) of 27 with pleural biopsy demonstrated chronic granulomatous inflammation with or without caseous necrosis. Of these 27 patients, PCR was positive in 12 (44.4%). A higher proportion (70.4%) of patients with TB pleurisy was diagnosed when PCR was combined with biopsy results.ConclusionThese data indicate that PCR alone has limited value in diagnosis of TB pleurisy with negative smear. However, when used in combination with pleural biopsy, it can be used to increase early detection of TB pleurisy in such patients.