Polymerase chain reaction targeting insertion sequence for the diagnosis of extrapulmonary tuberculosis

Diagnosis of extrapulmonary tuberculosis (EPTB) is difficult using conventional diagnostic methods. This study was conducted to evaluate the use of polymerase chain reaction (PCR) in diagnosis of definitive and probable extrapulmonary tuberculosis patients, and to assess the performance of insertion sequence (IS) 6110 based PCR assay as compared to conventional culture by Lowenstein-Jensen (LJ) method for the diagnosis of EPTB.

A total of 178 non repeated clinical specimens were collected from clinically suspected extrapulmonary tuberculosis patients. The specimens included 59 ascitic fluid, 54 pleural fluid, 25 cerebrospinal fluid (CSF), 12 fine needle aspiration (FNA), 8 urine, 7 pus, 6 synovial fluid, 2 skin tissue, one pericardial fluid, one liver abscess, one pancreatic cyst fluid, one omental biopsy and one semen sample. All these clinical samples were subjected to Ziehl-Neelsen staining (ZN) for acid fast bacilli (AFB) and culture on LJ medium. PCR was performed by targeting 123bp fragment of insertion sequence IS6110 of Mycobacterium tuberculosis (MTB).

Of the 178 specimens, 10 (5.61%) were ZN smear positive for AFB, six (3.37%) were L-J culture positive from 10 AFB smear positive cases and 48 (26.96%) were PCR IS 6110 positive for M. tuberculosis.

PCR using IS6110 primer was able to pick up more EPTB patients compared to conventional L-J culture method for detection of M. tuberculosis. False positive PCR IS6110 in three CSF samples may be due to latent TB infection which was limitation in this study.