Comparison of conventional diagnostic modalities, BACTEC culture with polymerase chain reaction for diagnosis of extra-pulmonary tuberculosis

This study attempts to determine and compare the sensitivity, specificity and turnaround time of conventional diagnostic modalities, BACTEC culture and polymerase chain reaction test for diagnosis of extra-pulmonary tuberculosis. One hundred clinically suspected patients of extra-pulmonary tuberculosis were studied. Specimens from these patients were processed for Ziehl-Neelsen (ZN) stain and culture for M. tuberculosis was done with inoculation on Lowenstein-Jensen (LJ) medium as well as the BACTEC MGIT 960 TB system. All the samples were processed for PCR amplification with primers targeting 123 bp fragment of insertion element IS6110 sequence of M. tuberculosis complex. Out of the hundred extra- pulmonary samples processed, 5% were positive by ZN staining, 15% were positive by both LJ culture and BACTEC MGIT 960 TB culture and 70% were positive by PCR. Those samples positive by ZN smear, LJ culture and BACTEC culture were all found to be 100% positive by PCR. The mean detection time for M. tuberculosis was 23.13 days by LJ Medium culture, 9.86 days by BACTEC MGIT 960 TB culture and less than one day by PCR. PCR as a diagnostic tool is more sensitive and useful in diagnosis of extra-pulmonary form of tuberculosis when compared to conventional methods or BACTEC culture by definitely shortening the time with early initiation of anti-tubercular treatment and can prevent disease progressing towards irreversible tissue damage.