Utility of GeneXpert in Diagnosis of Multidrug-resistant Extrapulmonary Tuberculosis

Abstract

ABSTRACT Background: The Xpert Mycobacterium tuberculosis (MTB)/rifampicin (RIF) assay (GeneXpert) is a rapid semi-quantitative nucleic acid amplification test with established role in the diagnosis of pulmonary tuberculosis (PTB) and multidrug-resistant (MDR) PTB. We determined the performance of the GeneXpert assay for the diagnosis of extrapulmonary tuberculosis (EPTB) MDR cases. Aims and objectives: To study the role of GeneXpert in the diagnosis of EPTB MDR. Materials and methods: A retrospective study was conducted over a period of 2 years at a tertiary care hospital after Ethics Committee permission. Data of 44 consecutive patients of diagnosed EPTB MDR were retrieved for GeneXpert and culture drug susceptibility test (DST). Sensitivity of GeneXpert in the diagnosis of EPTB MDR was calculated comparing culture DST results. Results: Various EPTB MDR cases studied were lymph node TB (n = 23) 51%, pleural effusion (n = 14) 32%, central nervous system TB/spinal TB/psoas abscess/gluteal abscess (n = 7) 17%. Sensitivity for GeneXpert was found to be 91.30, 57, 100% respectively. True positive and false negative were 36 and 8 cases respectively. The overall sensitivity of GeneXpert in diagnosing EPTB MDR was 81.80%. The sensitivity among lymph node, pleural effusions, and spinal/psoas abscess/gluteal abscess was 91.30, 57.14, and 100% respectively. Conclusion: GeneXpert sensitivity for the diagnosis of EPTB MDR varied with site of extrapulmonary involvement, with lower sensitivity in pleural fluid as compared with higher sensitivity among lymph node and spine TB. Nevertheless, given the rapid turnaround time and simplicity, it is a useful tool in the diagnosis of EPTB MDR when used in correct clinical context. Subsequent confirmation with culture DST, however, is recommended to diagnose false negatives.