Comparison of performance characteristics of laboratory diagnostic modalities in extrapulmonary tuberculosis

Abstract Background: A number of laboratory-based diagnostic modules are available for the diagnosis of extrapulmonary tuberculosis (EPTB), which vary greatly in terms of sensitivity and specificity. Methods: In this cross-sectional study, we conducted a comparative evaluation of the diagnostic efficacy of Xpert MTB/RIF testing and conventional techniques in clinically suspected cases of EPTB. Various extrapulmonary samples submitted at a tertiary care hospital in Northern India were subjected to Ziehl–Neelsen (ZN) staining, fluorescent staining, histopathological examination, conventional and automated liquid culture and Xpert MTB/RIF testing and the performance characteristics of diagnostic tests were calculated. Results: Out of the 141 cases included, diagnosis of EPTB was established in 33.3% of cases, with rifampicin resistance being detected in 8.5%. The prevalence was higher amongst females and younger subjects. Although highly specific, the sensitivity of ZN staining, fluorescent staining and culture on the Lowenstein–Jensen medium was low. Automated BacT/Alert culture and Xpert MTB/RIF assay expressed high sensitivity and diagnostic accuracy. Conclusions: Microscopic analysis and conventional culture methods may not be beneficial in the diagnosis of a paucibacillary disease like EPTB. Although having similar performance characteristics, the Xpert MTB/RIF may have the advantage over the automated BacT/Alert culture, of being easier to perform without an elaborate setup.