Acid-fast bacillus (AFB) tests
Explanation
AFB stands for acid-fast bacilli, bacteria that keep a special stain during laboratory testing. AFB tests look for these bacteria in a sample. These include the bacteria that cause tuberculosis (TB), but also other bacteria. Samples often contain mucus coughed up from the lungs; other samples may be used depending on where infection is suspected.
How do smear and culture differ?
A smear is examined under a microscope after staining. A culture tries to grow bacteria from the sample and can take several weeks. Further tests identify which bacteria are present. Tests for bacterial genetic material can also help identify TB more quickly.
Does a positive smear mean tuberculosis?
Not necessarily. Other bacteria can look similar with this staining method. The result needs further testing to identify the cause. A negative smear also does not rule out TB, because there may be too few bacteria in the sample to see.
Is this the same as a TB screening test?
No. AFB tests look for bacteria in a sample. TB skin tests and blood screening tests measure the immune system's response to TB bacteria. They do not by themselves show whether someone has active TB disease.
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