Diagnostic Value of Smear and Gene Xpert in Bronchoalveolar Lavage Fluid in Suspected Cases of Sputum Smear Negative Pulmonary Tuberculosis Patients

Hemax Gandhi, Abhishek Kumar, Pradeep Nirala, Mazher Maqusood, Chinmay Jethi, Chayan Chaplot, Arpit Goel, Manisha Rajak
Author(s)
1Resident, Department of Respiratory Medicine, Teerthanker Mahaveer Medical College & Research Centre, Delhi Road, Moradabad, Uttar Pradesh, India. 2Associate Professor, Department of Respiratory Medicine, Teerthanker Mahaveer Medical College & Research Centre, Delhi Road, Moradabad, Uttar Pradesh, India. 3Professor, Department of Respiratory Medicine, Teerthanker Mahaveer Medical College & Research Centre, Delhi Road, Moradabad, Uttar Pradesh, India. 4Professor & HOD, Department of Respiratory Medicine, Teerthanker Mahaveer Medical College & Research Centre, Delhi Road, Moradabad, Uttar Pradesh, India. 5Assistant Professor, Department of Respiratory Medicine, Teerthanker Mahaveer Medical College & Research Centre, Delhi Road, Moradabad, Uttar Pradesh, India

Abstract

Background: Diagnosis of sputum smear-negative pulmonary tuberculosis (PTB) remains challenging because of the low bacillary burden and poor sensitivity of conventional smear microscopy. Bronchoalveolar lavage (BAL) obtained during bronchoscopy provides an alternative respiratory specimen for microbiological confirmation. The objective is to compare the diagnostic performance of BAL AFB smear and BAL CBNAAT using MGIT culture as the reference standard in patients with suspected sputum smear-negative pulmonary tuberculosis. Material and Methods: This hospital-based observational cross-sectional study included 100 adult patients with clinically and radiologically suspected sputum smear-negative PTB. BAL specimens obtained by flexible bronchoscopy were analyzed using AFB smear microscopy, CBNAAT, and MGIT culture. Diagnostic performance was assessed by calculating sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), diagnostic accuracy, and Cohen's kappa coefficient. Results: BAL CBNAAT detected Mycobacterium tuberculosis in 37.0% of patients, compared with 12.0% by BAL AFB smear, while MGIT culture confirmed tuberculosis in 33.0% of cases. BAL CBNAAT demonstrated significantly higher sensitivity (87.9% vs. 25.0%), NPV (93.7% vs. 72.7%), overall diagnostic accuracy (88.0% vs. 73.5%), and stronger agreement with MGIT culture (κ=0.737 vs. 0.267) than BAL AFB smear. Although BAL AFB smear showed higher specificity (97.0% vs. 88.1%), its low sensitivity limited its diagnostic utility. Conclusion: BAL CBNAAT demonstrated superior diagnostic performance over BAL AFB smear for the diagnosis of suspected sputum smear-negative pulmonary tuberculosis. Its high sensitivity and diagnostic accuracy support its routine use as the preferred microbiological investigation in patients undergoing bronchoscopy, particularly when combined with mycobacterial culture for definitive confirmation.

Keywords: Pulmonary tuberculosis, Bronchoalveolar lavage, GeneXpert MTB/RIF, CBNAAT, Acid-fast bacilli smear, Mycobacterial culture.

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