Afb Smear (acid Fast Bacilli), Zn Stain

The Acid-Fast Bacilli (AFB) Smear Test is a laboratory test used primarily to detect the presence of acid-fast bacteria, which includes the Mycobacterium tuberculosis species responsible for tuberculosis (TB), as well as other mycobacteria. It involves examining a sample (typically sputum or other bodily fluids) under a microscope after it has been treated with special stains.

AFB tests are most often used to diagnose an active tuberculosis (TB) infection. They may also be used to help diagnose other types of AFB infections. These include:

• Leprosy, a once feared, but rare and easily treatable disease that affects the nerves, eyes, and skin. The skin often becomes red and flaky, with a loss of feeling.
• An infection similar to TB, such as Mycobacterium avium, that mostly affects people with HIVand others with weakened immune systems

You may need an AFB test if you have symptoms of active TB (TB disease). Which symptoms you have will depend on where in the body the TB bacteria are growing.

If TB disease is in the lungs (pulmonary), symptoms may include:

• Coughthat lasts for three weeks or more
• Coughing up blood and/or sputum
• Chest pain

Sample Collection

• Sputum (mucus from deep in the lungs) is the most common sample collected for the AFB smear test.
• It can also be collected from other sites like urine, cerebrospinal fluid (CSF), tissue, or gastric washings, depending on the clinical indication.

• Positive result: If AFB is seen, it indicates the presence of mycobacteria, and the test is considered positive for tuberculosis or other mycobacterial infections.
• Negative result: No AFB seen, suggesting that no mycobacteria are present in the sample. However, this does not completely rule out the presence of tuberculosis, especially if the infection is in an early or less active stage.

Advantages:

• Rapid and relatively inexpensive.
• Can provide immediate results in diagnosing active infections.