Polymerase chain reaction versus culture in the diagnosis of extrapulmonary tuberculosis-A comparative study

Introduction: Extrapulmonary tuberculosis (EPTB) accounts for approximately 40% of tuberculosis cases and is a significant health problem in both developing and developed countries. Extrapulmonary TB represents a greater diagnostic problem than pulmonary TB because it presents with less frequency and occurs with little liberation of bacilli, as well as the fact that it is localized in sites that are difficult to access. Materials & Methods: Samples from 60 clinically diagnosed cases of extrapulmonary TB were included in the study. All tissue samples were homogenized in a homogenizer. Thick viscous samples were subjected to NALC-NaOH method and all fluid samples were centrifuged. For DNA extraction, 200µl of the homogenized tissue or 200µl of centrifuged deposit from fluid samples were taken. PCR testing was done using IVD approved commercial kits. Deposit was also inoculated on LJ medium and Middlebrook-7H9 medium (MB7H9) aseptically. Results: A total of 60 samples from clinically diagnosed patients of extrapulmonary tuberculosis (EPTB) were studied. Maximum EPTB positivity was seen among pleural fluid samples followed by pus, CSF, tissue samples, ascitic fluid, synovial tissue, synovial fluid and pericardial fluid. The comparison of PCR versus culture was done and the sensitivity, specificity, PPV and NPV of PCR were 68%, 62.9%, 56.66% and 73.33% respectively considering culture as the gold standard. The comparison of duration taken for positivity by LJ and MB7H9 media showed that the mean duration of isolation on LJ and MB7H9 was 4.8 and 3.5 weeks respectively. Liquid culture showed growth earlier than the growth on solid medium. The period of maximum isolation on both media was 3rd week followed by 4th week. Conclusion: As PCR is a rapid method, and when used along with the conventional diagnostic methods increases the overall isolation rate of M. tuberculosis in the diagnosis of extrapulmonary tuberculosis.