AFB Smear and Culture

AFB Smear and Culture

Other names: Acid-fast bacillus, TB culture and sensitivity, Mycobacterial smear and culture
Specimen: Sputum, Gastric or bronchial washing (for children), Pleural fluid, Lung tissue


Your AFB Smear and Culture is

Absence of acid-fast bacilli indicates a negative test, though a single negative smear does not rule out the presence of mycobacterial infection.\r\n

Tuberculosis is caused by the bacteria Mycobacterium tuberculosis, or M. tuberculosis. The disease is detected by the presence of acid-fast bacilli (AFB), which are a tube-shaped bacteria. AFB can be counted under a microscopic when smeared on a slide and treated with an "acid-fast" process wherein a fluorescent dye stains the cell walls of the bacteria. Though other bacteria types can be detected the same way, most fall under the genus of Mycobacterium and are tested for when tuberculosis is suspected.
AFB smears are used primarily in the preliminary diagnosis of tuberculosis and related conditions. Three samples of sputum (deep cough specimen) are usually collected to increase probability of detection. The sample is smeared on a slide and stained with acid so that AFB can be counted under a microscope. Positive results are followed by a culture test (laboratory growing of bacteria). Molecular tests to detect genetic mycobacteria material may also follow to confirm diagnosis, plus tests to confirm or exclude disease resistance.
AFB smear and culture are ordered when symptoms or screening tests suggest a lung infection has been caused by tuberculosis, and to monitor the effectiveness of TB treatments for patients already diagnosed. Tuberculosis was a rare disease for decades but resurged in the 1980s concurrently with the spread of HIV. An immune system suppressed by HIV/AIDS has difficulty controlling TB bacteria, increasing the likelihood of acquiring the disease and spreading the infection. TB is a leading killer of people infected with HIV. Several strains of M. tuberculosis have proven resistant to antibiotics, further increasing risk of contagion. The CDC reports that one third of the world's population is infected with TB, with approximately 1.4 million TB-related deaths worldwide in 2011. In the U.S., a total of 10,528 were reported in 2011 (a 5.8% decline from 2010).