Introduction
An AFB culture is conducted to determine the presence of tuberculosis (TB) or other mycobacterial infections, such as leprosy, and a TB-like illness that affects individuals with HIV/AIDS. Healthcare professionals collect a sample of the phlegm or sputum or a small amount of tissue to perform the AFB culture. They place the sample in a specialized container with the necessary nutrients for bacterial growth and monitor it over several weeks to see if the bacteria develop. If bacterial growth is detected, this indicates mycobacterial infection.
What Is the Requirement of This Test?
There are many reasons to perform this test:
-
Firstly, a person is experiencing symptoms of a lung infection, such as chronic cough, coughing up blood, weight loss, fever, chills, and fatigue.
-
Secondly, they have tested positive for TB through either a skin or blood test, and they are at high risk of exposure to TB or the development of active disease. This includes individuals with weakened immune systems due to HIV/AIDS or another condition. People who have spent time in hospitals, nursing homes, or prisons are also at an elevated risk.
-
Thirdly, they are displaying symptoms of extrapulmonary TB, a condition where TB is present outside of the lungs. Symptoms change depending on the site of infection. While many associate TB with lung disease, it can also manifest in other parts of the body. For instance, if it infects the spinal cord, it can lead to back pain and paralysis. In the kidneys, it often results in blood in the urine.
-
Fourthly, they have a medical condition such as HIV/AIDS that makes them more susceptible to TB. If a person has also had close contact with someone who has TB, healthcare providers will want to perform this test.
-
Finally, the healthcare providers may administer this test periodically if the person is undergoing treatment for TB. This is to observe the effectiveness of the treatment and determine whether a person is still contagious.
What Are the Indications of the AFB Test?
If someone is experiencing symptoms of active TB, they might require an AFB test. These symptoms may comprise:
-
Persistent cough (lasting for three weeks or more).
-
Coughing up sputum and/or blood.
-
Chest pain.
-
Fever.
-
Night sweats.
-
Unintended weight loss.
Active TB can lead to symptoms in various parts of the body apart from the lungs, with the symptoms varying based on the affected area,
-
Back pain.
-
Blood in the urine.
-
Headache.
-
Joint pain.
-
Weakness.
If someone possesses specific risk factors, they may require testing as they might be at a heightened risk of contracting TB. These risk factors may include:
-
Having had close contact with an individual diagnosed with TB.
-
Having a weakened immune system due to HIV or another ailment.
-
Residing or working in a location where there is a high incidence of TB infection. Such places comprise homeless shelters, nursing homes, and prisons.
What Is the Procedure?
To conduct both an AFB smear and an AFB culture, the healthcare provider will require a sample of the sputum, which is generally collected at the same time. To obtain sputum samples:
-
The patient will be requested to cough deeply and expectorate into a sterile container, usually for two or three consecutive days, ensuring there are enough bacteria for testing.
-
In case a patient encounters difficulty in coughing up sufficient sputum, the provider may administer a sterile saline (salt) mist that helps induce deeper coughing.
-
If they still face issues in producing enough sputum, the provider may perform a procedure called a bronchoscopy. During this procedure, the patient will receive medication to numb any pain. Subsequently, a thin, illuminated tube will be passed through the mouth or nose and into the airways to collect the sample using suction or a small brush.
What Does the Result Mean?
If the results of the AFB smear or culture are negative, it likely means the patient does not have an active TB infection. However, it is also possible that there were not enough bacteria in the sample for the healthcare provider to make a diagnosis.
A positive AFB smear suggests TB or another type of infection, but an AFB culture is needed to confirm the diagnosis. Since culture results can take a few weeks to come back, the provider may choose to begin treating the infection in the meantime.
A positive AFB culture indicates an active TB or another type of AFB infection, and the culture can identify the specific type of infection. After the diagnosis, the provider may order a "susceptibility test" on the sample to determine which antibiotic would be the most effective treatment.
What Additional Tests Could Be Performed Alongside This Test?
If the healthcare provider suspects pulmonary TB, a chest X-ray may be done to help with the diagnosis. However, it is not a definitive test. While waiting for the culture results, which usually take two to six weeks, a patient may be treated for TB if the healthcare provider suspects pulmonary TB. Rapid tests, such as an AFB smear and a nucleic acid amplification (NAA) test, are usually done first on a deep phlegm sample. These tests help the healthcare provider decide whether to isolate and treat the patient before the culture results are available.
The AFB smear shows the presence of acid-fast bacteria, but it does not identify the bacteria species or the best treatment for it. The NAA test, on the other hand, detects the genetic material of the bacteria and is recommended by the CDC when TB is suspected, and the test results may affect treatment decisions.
If the AFB culture is positive, a susceptibility test will be done to determine which antibiotic will be most effective in treating the disease. This is important because TB bacteria are often resistant to some of the commonly used antibiotics.
Conclusion
The AFB culture test is a diagnostic tool used to determine the presence of mycobacterial infections, such as tuberculosis. It is performed by collecting a sample of sputum or tissue and placing it in a specialized container to monitor bacterial growth. A positive result indicates an active mycobacterial infection that requires further testing and treatment. The test is recommended for individuals displaying symptoms of active TB or with specific risk factors, and additional tests such as chest X-rays, AFB smears, and NAA tests may be performed to aid diagnosis and treatment decisions.
