Comparative evaluation of IS6110 PCR via conventional methods in rapid diagnosis of new and previously treated cases of extrapulmonary tuberculosis

In developing countries the diagnosis of extrapulmonary tuberculosis (EPTB) is a major burning challenge. EPTB encounters many problems like pauci-bacillary nature, inadequate specimen volume. All the limitations reflect in the poor contribution of conventional bacteriological technique in the establishment of diagnosis of EPTB. Nucleic acid amplification methods are rapid and sensitive has modified strategies for the detection of mycobacterial DNA. A fragment of DNA of 123bp belonging to insertion sequence IS6110 based on specific gene of Mycobacterium tuberculosis complex was amplified by polymerase chain reaction (PCR) for the rapid diagnosis of EPTB. The present study was to comparative evaluation of IS6110 PCR via conventional methods in the rapid diagnosis of new and Previously treated cases of extra pulmonary tuberculosis. Four hundred fifty specimens were collected from suspected cases of EPTB were processed for Mycobacteria by Zeihl Neelson (ZN) staining and BACTEC culture for M. tuberculosis. All the specimens were also processed for IS6110 based PCR amplification with primers targeting 123 bp fragment of insertion element IS6110 of M. tuberculosis complex. We found significant difference was seen in sensitivities of different tests. Of these 450 specimens, 60 (13.4%) were positive for AFB by ZN staining, 202 (45%) for BACTEC culture and IS6110 PCR were positive for M. tuberculosis complex in 283 (63%) specimens (p< 0.05). However, there was no significant difference (p< 0.05) as far as specificity of different tests. We found that IS6110 PCR has higher sensitivity than smear microscopy and BACTEC culture in both cases of new cases as well as in previously treated cases. IS6110 PCR can be highly useful in diagnosis of new and treated cases of EPTB. It may facilitate therapeutic decisions for those with suspected of EPTB.