Bronchial Washing for AFB

Function

The Bronchial Washing for Acid-Fast Bacilli (AFB) test is a critical diagnostic tool used to detect the presence of mycobacteria, most notably Mycobacterium tuberculosis, the causative agent of Tuberculosis (TB). Bronchial washing involves instilling sterile saline into a specific segment of the lung during a bronchoscopy and then suctioning it back out. This process collects cells, secretions, and potential pathogens from the lower respiratory tract that might not be present in a standard expectorated sputum sample.

Why it is Ordered

Clinicians order this test when a patient exhibits symptoms suggestive of pulmonary TB—such as chronic cough, night sweats, weight loss, and hemoptysis—but cannot produce adequate sputum, or when previous sputum smears were inconclusive. It is also used to diagnose Non-Tuberculous Mycobacteria (NTM) infections, which can mimic TB symptoms, particularly in immunocompromised individuals or those with underlying lung disease like COPD or bronchiectasis.

Associated Conditions

• Pulmonary Tuberculosis: The primary target of the AFB smear and culture.
• NTM Lung Disease: Caused by environmental mycobacteria like M. avium complex.
• Miliary Tuberculosis: A disseminated form of TB that may require deep sampling for detection.
• Immunocompromised States: Patients with HIV/AIDS are at higher risk for atypical mycobacterial presentations requiring bronchial washing for definitive diagnosis.

Procedure and Detection

The sample undergoes Ziehl-Neelsen or Kinyoun staining. The 'acid-fast' property refers to the ability of these bacteria to resist decolorization by acids during staining due to the high lipid (mycolic acid) content in their cell walls. A positive smear indicates an active infection and high potential for transmission.