Diagnostic Utility of GeneXpert MTB/RIF in Extra-Pulmonary Tuberculosis: A Retrospective Study from a Tertiary Care Centre in Western India

Extra pulmonary tuberculosis accounts for a sizeable fraction of tuberculosis cases in India. It is an enigmatic disease with a protean presentation and low bacillary load, posing a challenge to timely diagnosis. Rapid diagnosis is of prime importance in initiating early treatment and halting the spread of drug-resistant organisms. GeneXpert MTB/RIF assay, or CBNAAT, simultaneously detects Mycobacterium tuberculosis and its resistance to rifampicin in a variety of extrapulmonary specimens.

Objective: To assess the diagnostic utility of GeneXpert MTB/RIF in suspected EPTB and specimen-wise positivity with rifampicin resistance patterns.

Materials and Methods: This is a retrospective observational study conducted among a tertiary care hospital in Rajkot, Gujarat, from September 2022 to September 2024. A total of 434 extrapulmonary specimens were lymph node aspirates, pus, pleural fluid, cerebrospinal fluid, ascitic fluid, and synovial fluid examined by GeneXpert MTB/RIF. The demographic and clinical data along with laboratory data were retrieved from the records. Descriptive statistics and chi-square testing were conducted to evaluate the association of MTB positivity with HIV status and sample type.

Results: MTB was positive in 92 out of 434 samples (21.2%). The highest rate of positivity was seen in pus/cold abscess and lymph node aspirations, and the lowest was seen in serous fluids. The rate of MTB positivity was slightly higher among HIV-positive patients than among HIV-negative patients, but the difference was not statistically significant (p = 0.20). There was a statistically significant relationship between the type of specimens and the rate of MTB positivity (p < 0.001). Resistance to rifampicin was seen in 12 out of 92 samples of MTB-positive specimens, mostly from the lymph node and cerebrospinal fluids.

Conclusion: GeneXpert MTB/RIF is a fast and accurate diagnostic test with varying sensitivity for EPTB diagnosis according to the type of specimen being tested. The resistance results for rifampicin support early initiation of effective therapy and TB control activities within high-prevalent countries