Polymerase Chain Reaction Detection of Mycobacterium Tuberculosis from Sputum

Tuberculosis has remained to be a major public health problem in Nepal. The risk of spread of infection and emergence of drug-resistant strain has created the need for a rapid, sensitive and specific diagnostic test. In addition, clinically suspicious cases that do not give positive result in conventional laboratory test need more sensitive test for diagnosis. In order to evaluate the possibility of incorporation of Polymerase Chain Reaction (PCR) in the diagnosis of tuberculosis, we performed a comparative study of PCR to detect Mycobacterium tuberculosis in sputum specimens, against Ziehl-Neelsen (Z-N) stain and culture as a standard method. A total of 103 specimens were subjected to Z-N staining, culture and PCR for detecting Mycobacterium tuberculosis. Of these, 19 were positive by Z-N stain, 26 by PCR and 25 by culture. Four stain negative specimens showed positive result in both culture and PCR. Two specimens of stain and culture positive were PCR negative. Five specimens showed positive result only with PCR. Two culture positive specimens gave negative results by both Z-N stain and PCR. Sensitivity, specificity, positive predictive value and negative predictive value of PCR which were 84%, 93.5%, 80.8% and 94.9% respectively. This study showed that there is no need for PCR test for the smear positive cases. However, PCR could be a possible diagnostic tool for the confirmation of the smear negative cases that show clinical symptoms of TB.