Definition

This test is to help diagnose tuberculosis (TB) and infections caused by other Mycobacterium species, these species are known as acid-fast bacilli (AFB). This is because Mycobacteria are a group of rod-shaped bacteria (bacilli) that can be seen under the microscope after a staining procedure where the bacteria retain the color of the stain after an acid wash (acid-fast). 

AFB smear is done by placing a person’s sputum that is stained to detect the acid-fast bacteria, a microscope will be used to detect it. Another method is AFB culture; the sample is taken into the lab and placed in a special environment to encourage the growth of the bacteria. However, the AFB culture takes a long time to detect an infection because the bacteria will need 9-10 weeks to grow. 

Procedure

The first step is to obtain the patient’s sputum (phlegm), sputum is the mucous that we cough up from deep inside our lungs. The sputum will be collected in sterile cups. 

Usually three sputum samples are needed. You will be required to come in the morning on three different days. Do not worry if you are unable to produce sputum, a bronchoscope will be used to collect the fluid during a procedure known as bronchoscopy. It is done after spraying local anesthetic onto the patient’s upper airway, the practitioner then inserts a tube into the bronchi and smaller bronchioles and aspirate fluid samples for testing. 

These sputum samples will be then sent to the lab for AFB smear and AFB culture test. 

Result

The result will come back as either positive or negative.