Diagnosis of Extrapulmonary tuberculosis by cartridge-based nucleic acid amplification test (CBNAAT) and detection of rifampicin resistance on fine-needle aspiration samples: An institution-based study

Abstract

Background: Extrapulmonary tuberculosis (EPTB) is still a major health problem in developing countries. Diagnosis of EPTB is difficult due to paucity of acid-fast bacilli in clinical specimens. Objectives: To study the diagnostic role of cartridge-based nucleic acid amplification test (CBNAAT) and rifampicin resistance in EPTB on fine-needle aspiration samples. Materials and Methods: It is a prospective study comprising 79 patients of clinically suspected EPTB cases for 1 year duration. All patients underwent fine-needle aspiration cytology (FNAC) with Ziehl–Neelsen (ZN) staining followed by CBNAAT for confirmation of tuberculosis (TB) and to detect rifampicin resistance. Data have been collected and analyzed regarding sensitivity, specificity, positive predictive value, and negative predictive value of FNAC in comparison with CBNAAT. Results: Out of 79 patients, 47 (59.49%) patients were male and cervical lymph node was the most common site of aspiration (42, 52.16%). Granuloma with necrosis (38, 48.10%) followed by necrosis only (14, 17.72%) were the common findings on FNAC. Out of 79 suspected EPTB patients, CBNAAT confirmed 62 patients as having TB. Specificity of FNAC with ZN staining was 100.0%; however, sensitivity was low (43.55%) compared to CBNAAT. Only three cases were detected as rifampicin resistant. Conclusion: Compared to FNAC, CBNAAT has very good sensitivity and specificity in the diagnosis of EPTB. It has also as added advantage of detecting rifampicin resistance at the same time. CBNAAT should be used for diagnosis of EPTB wherever the facility is available.

Keywords

• cartridge-based nucleic acid amplification test (cbnaat)
• extrapulmonary tuberculosis
• fine-needle aspiration cytology
• rifampicin resistance
• ziehl–neelsen staining