This test is done to detect and identify infections caused by Mycobacterium tuberculosis, the cause of tuberculosis (TB), and other Mycobacterium species, which are known as acid-fast bacilli (AFB). When you have signs and symptoms of a lung infection, such as a chronic cough, weight loss, fever, chills, and weakness, that may be due to TB or a nontuberculous mycobacterial (NTM) infection; when you have a positive TB screening test and you are in a high-risk group for progressing to active disease; when you have a skin or other body site infection that may be due to mycobacteria; when you are undergoing treatment for TB. There are a several types of AFB that may be detected with this testing; however, the most common and medically important ones are members of the genus Mycobacterium. AFB cultures to grow the bacteria are set up at the same time as the AFB smears. Though more sensitive than AFB smears, results of cultures may take days to several weeks.
No test preparation is needed, except to rinse the mouth with water before collecting the sputum sample. AFB testing may be used to detect several different types of acid-fast bacilli, but it is most commonly used to identify an active tuberculosis (TB) infection.
If your results on an AFB smear or culture were negative, you probably don't have active TB. But it could also mean there weren't enough bacteria in the sample for your health care provider to make a diagnosis.
If your AFB smear was positive, it means you probably have TB or other infection, but an AFB culture is needed confirm the diagnosis. Culture results can take several weeks, so your provider may decide to treat your infection in the meantime.
If your AFB culture was positive, it means you have active TB or another type of AFB infection. The culture can identify which type of infection you have. Once you have been diagnosed, your provider may order a "susceptibility test" on your sample. A susceptibility test is used to help determine which antibiotic will provide the most effective treatment.
If you have questions about your results, talk to your health care provider.