Importance of polymerase chain reaction in diagnosis of pulmonary and extra-pulmonary tuberculosis

ABSTRACT

Pakistan ranks 8[th] on the list of 22 high-burden tuberculosis [TB] countries in the world according to the World Health Organization's [WHO] Global Tuberculosis Control 2009. Including other reasons the main cause is improper and late diagnosis of the disease. PCR may play an important role to control the disease with its rapid, sensitive and specific diagnosis. But in Pakistan due to lake of knowledge about this latest technique we are not using this technique appropriately. Clinicians still trust on conventional methods of TB diagnosis, which are time consuming or insensitive. The present study was arranged to highlight the importance of PCR in TB diagnosis in pulmonary and extra-pulmonary cases and its comparison with conventional methods. Samples obtained from 290 patients of suspected TB [pulmonary or extra-pulmonary] were subjected to ZN smear examination, LJ medium culture and PCR test by amplifying 541bp fragment of Mycobacterium tuberculosis complex genome. The present prospective study is performed at Shalamar Hospital Lahore from November 2008 to November 2010. A distinctly difference was observed in the test results done by PCR and other conventional techniques in pulmonary or extra-pulmonary tuberculosis samples [p<0.001]. The sensitivity of different tests was 68.62% for PCR, 26.90% for LJ medium culture, and 14.14% for ZN smear examination [p<0.05]. However, there was no significant difference between different tests as for as specificity was concerned. PCR test sensitivity in pulmonary and extra-pulmonary clinical samples was 78.34 and 61.76% respectively, being significantly higher [p<0.05] when compared with sensitivity of other tests. The mean detection time for M. tuberculosis was 25 days by LJ medium culture and less than 1 day by smear examination and PCR test. PCR test is more sensitive than ZN smear examination and LJ medium culture for the diagnosis of TB in pulmonary and extrapulmonary clinical samples