Sputum for AFB Stain (Acid-Fast Bacillus Staining Test)
The AFB (Acid-Fast Bacillus) stain test is used to detect Mycobacterium tuberculosis (TB) and other mycobacteria in a sputum sample. It helps diagnose tuberculosis (TB) and related infections.
Why is the Test Done?
A doctor may order this test if a patient has:
✅ Persistent cough lasting more than 2 weeks
✅ Fever, night sweats, and weight loss
✅ Blood in sputum (hemoptysis)
✅ Chest pain and difficulty breathing
✅ Suspicion of pulmonary tuberculosis (TB)
How is the Test Done?
1. Sample Collection:
- The patient is asked to cough deeply to produce sputum (mucus from the lungs).
- The sample is collected in a sterile container (early morning samples are preferred).
- At least 2–3 consecutive samples over 3 days are usually required for accuracy.
2. Laboratory Analysis (Ziehl-Neelsen Staining or Fluorescent Stain):
- The sputum sample is spread on a slide and stained with Ziehl-Neelsen stain or Auramine-Rhodamine fluorescent stain.
- The slide is examined under a microscope for Acid-Fast Bacilli (AFB).
- If AFB are present, they appear bright red against a blue background in Ziehl-Neelsen staining.
Test Results Interpretation
| Result | Interpretation |
|---|---|
| AFB Positive | Likely tuberculosis (TB) or other mycobacterial infection |
| AFB Negative | No mycobacteria detected (but TB cannot be ruled out, further tests may be needed) |
🔬 If Positive, further tests may be done:
- Sputum Culture (confirms TB and detects drug resistance)
- GeneXpert/CBNAAT (detects TB DNA and drug resistance)
- Chest X-ray or CT scan (for lung damage assessment)
Next Steps if TB is Confirmed
💊 Anti-TB Medications (ATT – 6 months or longer treatment)
😷 Isolation in active TB cases (to prevent spread)
🍎 Proper nutrition & hydration for recovery