Role of bronchoalveolar lavage cartridge-based nuclear acid amplification test in the diagnosis of sputum smear-negative pulmonary tuberculosis

Abstract

Background Approximately 40–60% of clinical and radiological suspected cases of pulmonary tuberculosis (PTB) will have sputum smear result negative for acid-fast bacilli (AFB). Establishing early diagnosis and starting treatment early can have significant effect on morbidity and mortality in these patients. Bronchoalveolar lavage (BAL) samples obtained by bronchoscopy can be tested with cartridge-based nuclear acid amplification test (CBNAAT) for rapid diagnosis of sputum smear-negative PTB cases. Objectives To assess the role of BAL CBNAAT in the early diagnosis of sputum smear-negative PTB cases. Patients and methods A total of 112 patients with clinicoradiological findings suggestive of PTB with two consecutive sputum smear-negative results for AFB were enrolled in the study. BAL samples were subjected to Ziehl–Neelsen staining, CBNAAT (Xpert MTB/Rif; Cepheid), and liquid culture by mycobacteria growth indicator tube method as standard reference. Sputum samples from the same patients were also cultured. Results BAL samples were positive for AFB on Ziehl–Neelsen staining in 64.2% of smear-negative patients. CBNAAT was positive in 75.8%, whereas mycobacteria growth indicator tube was positive in 76.7% as compared with sputum culture positivity, which was positive in 19.6% of patients. Sensitivity and specificity of CBNAAT were 96.51 and 86.3%, respectively, when compared with culture results. Overall, 76.7% of patients were diagnosed as having culture-positive PTB. Conclusion BAL CBNAAT is useful in the early diagnosis of sputum smear-negative PTB, thus reducing the morbidity and mortality among these patients.