EVALUATION OF SEROLOGICAL AND MOLECULAR METHODS OVER CONVENTIONAL METHODS IN DIAGNOSIS OF PULMONARY AND EXTRA PULMONARY TUBERCULOSIS

Despite advances in field of microbiology, diagnosis of Tuberculosis remains a challenge. Diagnosis of Extrapulmonary tuberculosis is more problematic due to low bacillary load in the specimen and difficulty in obtaining the specimen from the site of lesion in many cases. PCR and its modifications are a boon in diagnosis of tuberculosis in such cases. But serological methods like ELISA are still the first choice of small laboratories in India. AIM: Comparative evaluation of serological and molecular methods over conventional methods in diagnosis of extrapulmonary and pulmonary tuberculosis. METHODS: 170 different clinical specimens suspected of tuberculosis, (100 pulmonary and 70 Extrapulmonary) were examined by PCR using MPB 64 primer, culture and microscopy. All specimens were processed using USP methodology for inhibitors free PCR. TB Ig G, Ig M and Ig A was determined using PATHOZYME MYCO Kit. Response to ATT on clinical follow up was considered as gold standard. RESULTS: Total pulmonary specimens found positive by any of the four tests was 87 (out of 100) while that for extrapulmonary samples was 63(out of 70). For Pulmonary Specimens the diagnostic accuracy of microscopy was 88.3%, for culture 88.3%, for ELISA 67.4% and for PCR 94.1%. For extrapulmonary samples the diagnostic accuracy of microscopy was 30.1%, for culture 49.2%, for ELISA 44.4% and for PCR 87.3%. CONCLUSION: As diagnosis by microscopy and culture are sensitive and specific, for pulmonary specimens, PCR should be kept reserved for clinically probable cases found negative by conventional tests. For Extrapulmonary specimens PCR can be used as an effective screening tool as conventional methods are mostly negative. ELISA was found to have no role in diagnosis of pulmonary TB. For Extrapulmonary TB ELISA can be used as an adjunct tool but results should be interpreted with utmost caution after full evaluation of the patient both clinically and radiologically.