EFFICACY OF GENE XPERT MTB/RIF ASSAY AND AFB CULTURE IN DIAGNOSIS OF MYCOBACTERIUM TB COMPLEX ON EBUS TBNA

Abstract

SESSION TITLE: Tuesday Abstract Posters SESSION TYPE: Original Investigation Posters PRESENTED ON: 10/22/2019 01:00 PM - 02:00 PM PURPOSE: Rationale – Tuberculosis and Sarcoidosis are two clinical entity that share same clinical, radiological and pathological features and differentiating between two might be an arduous task. As cultures for M. Tuberculosis in tissue specimens have prolonged turn-around times, rapid molecular methods such as MTB. Rif system has shown great promise in rapid diagnosis of tuberculosis through detection of DNA of M. Tuberculosis and concurrent identification of major mutation that confers rifampicin resistance. We aim to evaluate both efficacy and role of Xpert MTB / RIF Assay and Mycobacterium TB Culture for diagnosis of TB using EBUS TBNA samples in patients with intra-thoracic granulomatous lymphadenopathy. METHODS: This was a retrospective study of randomly selected 100 patients who underwent EBUS TBNA for intra-thoracic granulomatous lymphadenitis with Gene Xpert MTB / RIF Assay and diagnosed with either Tuberculosis or Sarcoidosis RESULTS: EBUS TBNA procedures were performed and a diagnosis of Sarcoidosis (n 17) or Tuberculosis (n 83) was made in 100 patients. Histological results with grades I to II were seen in 74 patients and grade III in 26 patients respectively. Necrotising granulomas were found in 26 / 83 (31.32%) while Non-necrotising granulomas were found in 57 / 83 (68.67%) patients diagnosed with Tuberculosis. Mycobacterium TB Culture was performed in 72 patients diagnosed with Tuberculosis and was positive in 11 patients – 09 / 26 Necrotising Granuloma vs 02 / 57 Non-necrotising Granuloma (34.61% vs 3.5%, P = 0.010). Gene Xpert MTB / RIF Assay were performed in 20 / 83 patients diagnosed with Tuberculosis and was positive in 4 patients – 01 / 07 Necrotising Granuloma vs 03 / 13 Non-necrotising Granuloma (14.30% vs 23.10%, P = 0.547). The Diagnostic Accuracy of Xpert MTB / RIF Assay in diagnosis of Tuberculosis was 70% (95% CI 45.72% to 88.10%), Sensitivity 40%, Specificity 100%, Disease Prevalence 50%, PPV 100%, NPV 62.50%. Of 2 patients finally diagnosed with Sarcoidosis also showed a positive result of Xpert MTB / RIF Assay which possibly suggests casual link between TB and Sarcoidosis CONCLUSIONS: Gene Xpert MTB / RIF Assay can be useful in patients with suspected Pulmonary TB either AFB smear negative or positive due to its rapid and simultaneous detection of Rifampicin resistance and especially beneficial in patients with MDR TB and HIV associated TB. Xpert MTB / RIF Assay has good sensitivity and PPV in context of culture positive intra-thoracic TB lymphadenopathy and can provide immediate diagnosis of likely drug resistance specially in highly endemic area like India CLINICAL IMPLICATIONS: Positive Xpert MTB / RIF Assay with very low MTB detection but culture negative results need to be read cautiously and should be well correlated with clinical and treatment history of patient since Gene Xpert Assay amplifies any DNA, of live or dead bacilli and required to avoid false positive result DISCLOSURES: No relevant relationships by UMANG SHAH, source=Web Response