Bronchoalveolar Lavage CBNAAT in Sputum-Negative Presumptive Tuberculosis: Diagnostic Yield and Clinicoradiological Predictors in a High-Burden Tertiary Setting

Background: Patients with persistent clinicoradiological suspicion of pulmonary tuberculosis may remain negative on sputum smear microscopy and sputum CBNAAT, delaying confirmation and treatment.

Objective: To determine the diagnostic yield of bronchoalveolar lavage (BAL) fluid CBNAAT and identify clinical and radiological predictors of positivity.

Materials and Methods: This observational study enrolled 70 adults at a tertiary respiratory centre in Jodhpur, India. All had two sputum samples negative for acid-fast bacilli and one sputum sample negative on CBNAAT. Fibreoptic bronchoscopy with BAL was performed, and samples were tested by AFB smear, CBNAAT and mycobacterial culture. Diagnostic performance was estimated against the final composite diagnosis. Associations with BAL CBNAAT positivity were explored using univariate and multivariable logistic regression.

Results: The mean age was 45.04 ± 13.91 years and 45 (64.3%) participants were men. BAL CBNAAT was positive in 21/70 patients (30.0%; 95% CI 20.5-41.5), BAL culture in 24 (34.3%) and BAL AFB smear in 11 (15.7%). Pulmonary tuberculosis was the final diagnosis in 26 patients (37.1%). BAL CBNAAT showed 80.8% sensitivity, 100% specificity, 100% positive predictive value, 89.8% negative predictive value and 92.9% accuracy. Fever, loss of appetite and night sweats were associated with positivity on univariate analysis. Upper-lobe involvement (crude OR 5.00) and cavitation (crude OR 13.94) were strong radiological predictors; upper-lobe involvement remained independently associated after adjustment (adjusted OR 6.56, 95% CI 1.54-27.97; p=0.011). Bronchoscopy also established alternative diagnoses in 44 patients and caused only minor, self-limited complications.

Conclusion: BAL CBNAAT provides rapid, highly specific confirmation in a clinically challenging sputum-negative population. Culture remains complementary, while upper-lobe disease can help prioritize patients for bronchoscopy.