Medical Journal of The Islamic Republic of Iran (MJIRI)

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We investigated the use of DNA amplification by polymerase chain reaction (peR) for detection of Mycobacterium tuberculosis in 300 patients who were suspected of having pulmonary tuberculosis and compared the results with culture results which were performed in parallel with PCR. Two-thirds of each sample was processed for smear and culture by standard methods and one-third was prepared for DNA extraction, amplification and detection using Mycobacterium tuberculosis specific PCR primers. In this study 45 patients were positive for M. tuberculosis by PCR and probe hybridization (sensitivity and specificity 100%) whereas 42 patients (93%) exhibited growth of M. tuberculosis. Of 42 culture positive specimens 3 exhibited negative PCR results. Smear positivity rate for PCR positive specimens was 73.2%. For analysis of discrepant results 3 variables such as the source of specimen, the concentration of bacteria in the original specimen and the presence of inhibitor were examined. It was found that only 3 sputum specimens (6.6%) gave discrepant results, which were found to contain inhibitor of amplification. It remains to be shown whether positive PCR results in smear and culture negative patients mean false positivity or an early laboratory finding which predicts a subsequent reactivation of a prior tuberculosis infection or whether asymptomatic patients may carry PCR amplifiable Mycobacterium tuberculosis DNA without any clinical relevance.

Keywords: PCR, Mycobacterium tuberculosis, Sputum, Probe

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