AFB is Acid-fasting Bacillus, acid-fasting is the property of certain bacterial cells. The AFB Smear test is carried out when a person is suspected to have Tuberculosis. The tuberculosis infection is caused by the Mycobacterium tuberculosis AFB. The test is carried out by taking the sample from the patient and is the fastest yet effective tests available to detect tuberculosis. The negative test results means that the infection is not present in the patient. A positive AFB test result indicates the presence of mycobacteria in the sample. The negative sample may contain infection and is therefore the sample is still allowed to grow in the culture.