AFB in pleural fluid refers to acid-fast bacilli present in the fluid surrounding the lungs (pleural fluid). Their detection can be indicative of tuberculous pleuritis.
Understanding AFB and Pleural Fluid
- Pleural Fluid: This is the fluid found in the pleural space, which is the area between the lungs and the chest wall.
- Acid-Fast Bacilli (AFB): These are a group of bacteria that have a unique cell wall composition, making them resistant to decolorization by acid after being stained. The most clinically significant AFB is Mycobacterium tuberculosis, the bacteria that causes tuberculosis (TB).
AFB and Tuberculous Pleuritis
Tuberculous pleuritis is an inflammation of the pleura caused by Mycobacterium tuberculosis. According to the provided reference, the detection of Mycobacterium tuberculosis in pleural fluid, or pleural biopsy specimens, is the gold standard for diagnosis. This detection can be done via:
- Microscopy: Examining the fluid under a microscope to identify AFB.
- Culture: Growing the bacteria in a lab to confirm the presence of Mycobacterium tuberculosis.
The reference also mentions that the histological demonstration of caseating granulomas (a specific type of inflammation) in the pleura along with AFB is also indicative of tuberculous pleuritis.
Diagnostic Significance
Finding AFB in pleural fluid suggests a possible TB infection affecting the pleura. However, it's important to note that:
- AFB smear is not highly sensitive: A negative AFB smear does not rule out TB.
- Culture is more sensitive: Culture allows bacteria to multiply, increasing the chances of detection.
- Other tests may be needed: Pleural biopsy and other tests are often necessary to confirm the diagnosis.
