POLYMERASE CHAIN REACTION DETECTION OF MYCOBACTERIUM TUBERCULOSIS FROM SPUTUM

Abstract

ABSTRACT
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.

Key Words: Mycobacterium tuberculosis, Z-N stain, PCR, sensitivity, specificity.