Acid-fast bacilli (AFB) are a category of bacteria known to cause serious conditions such as tuberculosis (TB) and other mycobacterial infections, including leprosy. For individuals exhibiting symptoms suggestive of active tuberculosis, AFB tests are a crucial diagnostic tool. Tuberculosis, a severe bacterial infection primarily affecting the lungs but capable of spreading to other organs like the brain, spine, and kidneys, is caused by Mycobacterium tuberculosis. The bacteria are transmitted from person to person through respiratory droplets, such as those expelled during coughing or sneezing.
Tuberculosis can exist in two states: latent and active. In latent TB, the bacteria are present in the body but inactive. Individuals with latent TB are asymptomatic and cannot transmit the infection. Active TB, conversely, is characterized by the presence of symptoms and the ability to spread the infection to others.
AFB tests are specifically designed to detect AFB bacteria in sputum, a thick mucus expectorated from the lungs, distinct from saliva or spit. Several types of AFB tests are employed for identification:
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AFB Smear: This initial test involves spreading a sputum sample on a glass slide for microscopic examination. Providing preliminary results within 1-2 days, a positive AFB smear indicates a potential infection but is not definitive for a TB diagnosis.
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AFB Culture: For a definitive diagnosis, an AFB culture is performed. The sputum sample is sent to a laboratory to allow bacterial growth, amplifying the number of cells for testing. An AFB culture can confirm the presence of TB or other mycobacterial infections. However, it requires a longer incubation period of 6-8 weeks to cultivate a sufficient bacterial quantity for detection.
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Molecular Test (NAAT): This advanced test, utilizing Nucleic Acid Amplification Testing (NAAT), is often performed in conjunction with AFB smear and culture. NAAT is applied directly to sputum samples to rapidly detect TB bacteria. Importantly, if TB bacteria are detected, this test can also determine if the bacteria exhibit resistance to rifampicin, a commonly used antibiotic in TB treatment. The molecular test offers significantly faster results, typically within two hours.
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Susceptibility Test: Usually ordered alongside an AFB culture, a susceptibility test is crucial for determining the most effective antibiotic regimen to treat the infection. Mycobacterium tuberculosis can develop resistance to various anti-TB medications, making this test essential for guiding treatment decisions.
Alternative Names: AFB Smear and Culture, TB Culture and Sensitivity, Mycobacteria Smear and Culture, TB NAAT, Acid-Fast Bacillus Smear and Culture and Sensitivity, Mycobacterium tuberculosis Nucleic Acid Amplification Test.
