AFB Culture (Radiometric)

Function

The AFB (Acid-Fast Bacilli) Culture using radiometric methods (such as the BACTEC system) is designed to detect the presence of Mycobacterium tuberculosis and other non-tuberculous mycobacteria (NTM). The radiometric technique detects the metabolic activity of the bacteria by measuring the release of radioactive CO2 from a labeled substrate in the growth medium, allowing for much faster detection than traditional solid media cultures.

Why it is Ordered

This test is the 'gold standard' for diagnosing active Tuberculosis (TB). It is ordered for patients presenting with chronic cough, weight loss, night sweats, or abnormal chest X-rays. It is also used to determine the effectiveness of anti-TB treatment and to confirm that a patient is no longer infectious.

Associated Conditions

• Pulmonary Tuberculosis: The most common infection caused by M. tuberculosis.
• Extrapulmonary TB: Infection in the kidneys, spine, or brain.
• MAC Infection: Mycobacterium avium complex, often seen in immunocompromised individuals (e.g., those with HIV/AIDS).
• Leprosy: Caused by Mycobacterium leprae, though usually diagnosed via biopsy rather than culture.

Summary

Because mycobacteria grow very slowly, the radiometric culture is essential for early diagnosis, reducing the time to result from 6-8 weeks to as little as 1-2 weeks for positive samples.