Utility of the GeneXpert Mycobacterium tuberculosis/Rifampin (MTB/RIF) Assay on Paraffin-Embedded Biopsy Tissue Samples for Detecting Tuberculosis; Comparison With Histopathology

Introduction The Xpert Mycobacterium tuberculosis/Rifampin (MTB/RIF) assay is a qualitative nested real-time polymerase chain reaction (PCR) performed on the GeneXpert instrument system. Although, the utility of this technique for detecting tuberculosis (TB) in sputum and pus samples is well established, however, the usefulness of GeneXpert on biopsy samples is still a matter of debate. Therefore, in this study, we evaluated the utility of GeneXpert for detecting MTB in biopsy specimens diagnosed with TB. Methods A retrospective observational study was conducted at the Department of Pathology, Liaquat National Hospital and Medical College. The data collection period was between January 2016 and December 2018 over a period of three years. Specimens included trucut/incisional biopsies and lymph node excisions. Cases with a favoured histopathological diagnosis of TB were included in the study. The Xpert MTB/RIF assay was performed on the samples obtained from paraffin-embedded biopsy tissue material, and comparison of histological features with Xpert MTB/RIF assay was performed. Results A total of 114 cases were included in the study. The mean age of the patients was 40.53±16.83 years, and 57.9% of patients were male. 68.4% of cases were extra-nodal with the lung being the most common extra-nodal site. On histopathological analysis, caseation necrosis, epithelioid granulomas and Langhan's giant cells were present in 64.9%, 70.2%, and 59.6% cases, respectively. On GeneXpert PCR assay, MTB was detected in 26.3% cases. A significant association of MTB detection on Xpert PCR assay was noted with the presence of necrosis on histopathology. Conclusion In our study, we noted that the MTB detection rate by GeneXpert assay on histopathologically diagnosed cases of TB was only 26.3%, and the detection rate was significantly increased in the presence of caseation necrosis on a biopsy tissue sample. Despite the low detection rate due to rapid turnover time, GeneXpert assay is an excellent adjunctive tool for detecting MTB in paraffin-embedded tissue samples.