Sputum for Acid-Fast Bacilli (AFB)

Function

The Sputum for Acid-Fast Bacilli (AFB) test is a primary diagnostic tool used to detect the presence of mycobacteria, most notably Mycobacterium tuberculosis, the causative agent of tuberculosis (TB). Mycobacteria are characterized by a unique waxy cell wall containing mycolic acid, which resists traditional Gram staining but retains specialized dyes even after washing with acid-alcohol, hence the term 'acid-fast.'

Why it is Ordered

Physicians order this test when a patient presents with symptoms suggestive of pulmonary TB or other chronic lung infections. Symptoms include a persistent cough lasting more than three weeks, coughing up blood (hemoptysis), chest pain, unexplained weight loss, night sweats, and fever. It is also used to monitor the effectiveness of anti-tubercular treatment; a conversion from 'Positive' to 'Negative' indicates that the therapy is working and the patient is becoming less infectious.

Associated Conditions

• Tuberculosis (TB): The most common reason for a positive result.
• Nontuberculous Mycobacteria (NTM): Such as Mycobacterium avium complex (MAC), often seen in immunocompromised individuals or those with underlying lung disease like COPD.
• Leprosy: While primarily a skin/nerve disease (M. leprae), AFB staining is the gold standard for identification in various tissue types.

This test is vital for public health surveillance, as it helps identify infectious individuals who require isolation to prevent community spread.