Diagnosis of tuberculosis: the experience at a specialized diagnostic laboratory

This work describes the experience at a tuberculosis clinical laboratory where relatively new TB diagnosis technologies; nucleic acid detection of two target strands, IS6110 and devR, by PCR and microscopic observation drug susceptibility (MODS) were used. The LJ culture was the gold standard. This evaluation was done from August 2007 to July 2009 on 463 sputum samples of tuberculosis suspects at a specialized tuberculosis clinic in Delhi, India. None of the tests we evaluated can accurately detect the presence or absence of Mycobacterium tuberculosis in all the samples and smear microscopy was found to be the most reliable assay in this study. The PCR assay could detect down to 2 pg of H37Rv DNA. Sensitivity, specificity was 0.40, 0.60 and 0.19, 0.81 for smear positive (n = 228) and negative samples (n = 235) respectively. In the MODS assay, sensitivity, specificity of 0.48, 0.52 and 0.38, 0.76 was observed for smear positive and negative samples. Sputum smear microscopy had sensitivity of 0.77 and specificity of 0.70.