Role of PCR in the Diagnosis of Pulmonary and Extra-Pulmonary Tuberculosis

摘要

Introduction: Accurate and early diagnosis is needed for effective management of tuberculosis which remains to be one of the serious public health issues.Aim: To compare the IS6110 gene based Polymerase Chain Reaction (PCR) with conventional culture on Lowenstein Jensen media for the diagnosis of pulmonary and extra-pulmonary tuberculosis (EPTB).Materials and Methods: In a prospective study pulmonary and extra-pulmonary specimens from 100 patients clinically suspected with tuberculosis were processed by smear microscopy, culture and IS6110 based PCR following standard procedures. Among the cultured M. tuberculosis isolates, drug resistance to isoniazid and rifampicin was studied by line probe assay.Results: The positivity rates by smear microscopy, culture and PCR were 28(56%), 36(72%) and 37(74%) respectively for suspected pulmonary tuberculosis (PTB) (n=50) and 18(36%), 29(58%), 39(78%) for EPTB (n=50). Sensitivity and specificity of PCR for extra-pulmonary samples in comparison with culture as gold standard was 82.2% and 28.6% respectively but it was 92.1% and 82.2% respectively when clinical diagnosis was considered as gold standard. PCR helped to diagnose 10 extra cases (39 Vs 29) of EPTB when compared to culture. Resistance to isoniazid, rifampicin and multi-drug resistance was observed in 38.6%, 22.8% and 21% respectively. Turn-around-time for PCR was 24-48 hours when compared to culture positivity which is 4-6 weeks.Conclusion: PCR should be included especially in case of EPTB for timely diagnosis of cases of tuberculosis so that anti-tubercular treatment can be started in time to lower the morbidity of the disease.