Effectiveness of Xpert MTB/RIF for the diagnosis of extrapulmonary tuberculosis at various stand-alone laboratories in Delhi

Abstract Background Globally, EPTB accounts for 15% of the notified incident TB cases. Laboratory confirmation of EPTB is challenging and majority of the cases remain undetected for a longer time. A major breakthrough in the diagnosis of EPTB was the introduction of nucleic acid amplification tests (NAAT). One such test-the Xpert MTB/RIF assay also known as Cartridge based nucleic acid amplification test (CBNAAT) was endorsed by the Scientific and Technical Advisory Board of the WHO for the diagnosis of Tuberculosis. The present study was conduct to evaluate the outcome of various extrapulmonary samples tested in the year 2019 at different standalone NAAT laboratories in Delhi. Materials and methods A total of 20,238 samples consisting mainly of Pus (21.77%), Cerebrospinal fluid (CSF) (14.96%), Biopsies (13.87%), Pleural fluid (10.49%), Lymph node aspirations (FNAC aspirates) (6.75%), synovial fluid (0.54%) and gastric aspirates (26.4%) tested at 22 standalone NAAT laboratories were included in this study. Results Mycobacterium tuberculosis was detected in 3496 samples and resistance to rifampicin was detected in 329 of the samples. The overall yield of all the specimens combined was 17.2%. Highest yield was seen in Lymph nodes aspirates (FNAC) (36.0%), followed by pus (35.4%), tissues (15.7%), synovial fluid (13.5%), Endometrial tissues (10.7%), Pleural fluid (9.5%), Gastric aspirates (9.4%) and CSF (6.5%). The lowest yield was seen in Cavitary fluids (6.2%). Conclusion The results of this study highlight the usefulness of Xpert MTB/RIF assay in the diagnosis of EPTB. In particular, this assay proved to be of great utility while testing pus samples, tissue samples and lymph node FNACs.