The role of smear microscopy of induced sputum and bronchoalveolar lavage in the diagnosis of pulmonary tuberculosis in patients with initial smear-negative: A prospective study

Original Research


Introduction: Several studies have compared the diagnostic value of sputum induction (SI) with flexible fiberoptic bronchoscopy (FOB) in diagnosing pulmonary tuberculosis; however, these investigations yield an inconsistent conclusion. This study aims to evaluate the role of acid-fast bacilli (AFB) testing of SI and bronchoalveolar lavage (BAL) samples in suspected pulmonary tuberculosis cases.

Methods: A prospective study was conducted at the Department of Pulmonary in Cho Ray Hospital (Ho Chi Minh City, Vietnam) between October 2020 and May 2021. The study comprised 60 patients hospitalized with suspected pulmonary tuberculosis who had at least one negative AFB result from spontaneous sputum or gastric lavage. All participants underwent AFB testing of SI and BAL samples on the same day.

Results: Among 60 patients, 25 (41.7%) were diagnosed with pulmonary tuberculosis. Of the patients with pulmonary tuberculosis, 13 had positive AFB results, including four cases with both positive AFB SI and positive AFB BAL results. The sensitivity of AFB SI was significantly lower compared to that of AFB BAL (16% vs. 52%, p = 0.0027). The most common complication associated with the SI method was cough (15%). The proportion of patients able to provide sputum using the SI method was significantly higher than those with spontaneous sputum (p = 0.0499, McNemar test).

Conclusions: SI is a safe and effective method for collecting respiratory specimens, even from patients unable to expectorate spontaneous sputum. FOB should be reserved for suspected cases of pulmonary tuberculosis that are negative for AFB in spontaneous sputum, SI, and gastric lavage.

Graphical abstract