Extrapulmonary Tuberculosis: Is Cartridge Based Nucleic Acid Amplification Test More Superior to the Conventional Methods in Diagnosis?

Extrapulmonary Tuberculosis [EPTB] affects mainly lymph nodes, pleura, central nervous system, bones, gastrointestinal tract and genitourinary tract. Most commonly it presents as isolated lymphadenopathy and also as effusion in the body cavities. Tests to diagnose EPTB include Fine Needle Aspiration Cytology [FNAC], Acid Fast Bacilli [AFB] demonstration by Zeihl-Neelson [Z-N] stain and Cartridge Based Nucleic Acid Amplification Test [CBNAAT]. A retrospective record based study was conducted by taking the data of 100 clinically suspected EPTB patients who had undergone FNAC, CBNAAT and Z-N stain in Mandya Institute of Medical Sciences, Mandya, Karnataka. The study was conducted for a period of four months from March 2018 to June 2018 after taking approval from the Institutional Ethics Committee. The study showed 47 cases with FNAC findings favouring EPTB. Out of these 47 cases, 30 cases were CBNAAT positive. CBNAAT was positive in 5 cases out of 53 cases with negative FNAC findings. Among 35 CBNAAT positive cases, only 13 cases were AFB positive. To conclude, CBNAAT is rapid, accurate and simple test for early diagnosis of EPTB because of its high specificity and positive predictive value. CBNAAT can also detect the cases missed by FNAC and Z-N stain.