Management of Negative BAL AFB Smear in Suspected Tuberculosis

Initial Assessment and Treatment

The American Thoracic Society recommends collecting at least three sputum specimens for AFB smears and mycobacterial cultures as part of the diagnostic evaluation 2
The Centers for Disease Control and Prevention suggests considering nucleic acid amplification testing (NAAT) on respiratory specimens to provide rapid identification of M. tuberculosis 3
The American College of Chest Physicians recommends performing tuberculin skin test (TST) or interferon-gamma release assay (IGRA); a positive result supports the diagnosis of culture-negative pulmonary tuberculosis 1
Collecting postbronchoscopy sputum specimens may yield positive results even when BAL specimens are negative, as suggested by the Infectious Diseases Society of America 4, 5
The American Thoracic Society recommends considering additional diagnostic testing based on clinical features and differential diagnosis 2

The American College of Chest Physicians recommends initiating empiric treatment with isoniazid (INH), rifampin (RIF), pyrazinamide (PZA), and ethambutol (EMB) even when initial sputum smears are negative, for patients with high clinical suspicion of TB 1, 2
For patients with negative cultures but presumed pulmonary TB, the American Thoracic Society recommends performing thorough clinical and radiographic evaluation at 2 months of therapy 2
The American College of Chest Physicians suggests that for culture-negative TB, the continuation phase can be shortened to 2 months of INH and RIF (total 4 months of therapy) 2

The Centers for Disease Control and Prevention recommends that for HIV-infected patients, a more aggressive diagnostic and treatment approach may be warranted due to higher risk of rapid disease progression, however this fact is from a less preferred source and an alternative is: In patients with suspected miliary TB and negative induced sputum, bronchoscopic sampling should include bronchial brushings and/or transbronchial biopsy, as suggested by the Infectious Diseases Society of America 5

The Centers for Disease Control and Prevention warns against single-drug therapy or adding a single drug to a failing regimen, as this can lead to development of drug resistance 3
The American Thoracic Society notes that smear-negative cases represent approximately 17% of pulmonary TB cases in the US, and therefore TB diagnosis should not be excluded based solely on negative AFB smears 2