Significance of appropriate sampling in the diagnosis of tuberculosis [TB] - a comparison of different techniques

After years of decline, tuberculosis [TB] has re-emerged as a serious public health problem worldwide causing significant mortality and morbidity in developing countries like Pakistan, where the estimated incidence of TB is 181 per 10000. The present prospective study was conducted in Shalamar Hospital Lahore from January 2007 to October 2009. The objective was to compare the PCR results of specific site samples and blood of the same TB patient to see the validity of PCR results based on blood samples. Clinical samples obtained from 205 patients of suspected TB [pulmonary or extra-pulmonary] were subjected to ZN smear examination, LJ medium culture, and PCR test by amplifying 541 fragment of Mycobacterium tuberculosis complex genome. A highly significant difference was seen in the test results clone on samples obtained from specific site according to disease and blood samples of the same patient infected with pulmonary or extra-pulmonary tuberculosis. The sensitivity of different tests was found to be significantly different, which was 67.32 percent for PCR test, 27.81 percent for LJ medium culture and 12.20 percent for ZN smear examination. However, there was no significant difference between different tests as far as specificity was concerned. PCR test sensitivity in pulmonary and extra-pulmonary clinical samples was 77.15 and 61.6 percent respectively, being significantly higher, when compared with sensitivity of other tests. The mean detection time for M. tuberculosis was 24 days by LJ medium culture and less than 1 day by .smear examination and PCR test. We concluded that the PCR test is more sensitive than ZN smear examination and LJ medium culture for the diagnosis of TB in pulmonary and extra-pulmonary clinical samples. To get more accurate results PCR for TB diagnosis should be done on specific site samples. Blood samples are not appropriate for the diagnosis of TB by PCR when the PCR is clone on TB genomic DNA