Role of Polymerase Chain Reaction as a Diagnostic Tool in Pulmonary Tuberculosis

The rapid diagnosis of infectious diseases that represent a public health problem, like tuberculosis, is a challenging problem. The sensitivity of Polymerase Chain Reaction (PCR) makes it a potential diagnostic test for detection of Mycobacterium tuberculosis (M. tb) in samples with low bacillary load. A cross sectional study was carried out to determine the efficiency of PCR as compared to other routine diagnostics like smear microscopy and culture, amongst sputum samples and blood samples. Total 250 blood and sputum samples were collected from clinically suspected cases of pulmonary tuberculosis among HIV/AIDS patients. Sputum samples were stained with ZN stain, then decontaminated and cultured on LJ medium (gold standard) and PCR, whereas blood samples were processed only for PCR. Out of 250 cases, 49 were AFB smear positive (19.6%), 56 (22.4%) culture positive and PCR from sputum was positive in 69 (27.6%). The overall sensitivity and specificity of the PCR assay were 91.5% and 86.0% respectively and the positive and negative predictive values were 87.0% and 91.0% respectively. It also identified 13 smear negative and culture-negative cases as positive, whereas in case of blood sample (n=250), only 15 (6.0%) were PCR positive. The higher amount of TB positivity by PCR compared to culture & smear emphasize the role of PCR as a first line diagnostic tool in detection of pulmonary tuberculosis in sputum samples in HIV population as PCR is rapid, sensitive and cost effective compared to conventional diagnostic methods.