For an AFB (Acid-Fast Bacillus) test for Mycobacterium tuberculosis, common body fluids include sputum, cerebrospinal fluid (CSF), pleural fluid, urine, gastric washings, and synovial fluid, depending on the suspected site of infection; sputum is most frequent for lung TB, while other fluids help diagnose TB in other body parts, using techniques like Ziehl-Neelsen staining or fluorescent dyes under a microscope for rapid results