✍️ Edited by Farhan Ahmed, Editor, MedTestBD · Last updated: August 2026
What is the Sputum AFB Test?
The Sputum for AFB (Acid-Fast Bacilli) test examines a sputum sample under a microscope for the presence of acid-fast bacilli — bacteria that retain a specific red stain due to their waxy cell wall. The most important AFB in clinical medicine is Mycobacterium tuberculosis, the bacteria that causes tuberculosis (TB). This test is the most widely used front-line test for diagnosing pulmonary (lung) TB and is particularly critical in Bangladesh, where TB remains a major public health concern.
Why is the Sputum AFB Test Done?
- To diagnose pulmonary tuberculosis in patients with persistent cough, especially lasting more than 2–3 weeks
- To screen contacts of known TB patients who develop respiratory symptoms
- To monitor treatment response in patients already on anti-TB therapy — the AFB count should fall with successful treatment
- To confirm TB before starting treatment when chest X-ray findings suggest TB
- To diagnose other mycobacterial infections such as non-tuberculous mycobacteria (NTM)
Understanding AFB Smear Results
| Result | Interpretation |
|---|---|
| Negative (No AFB seen) | TB not detected — but does not rule out TB if clinical suspicion is high |
| Scanty (1–9 AFB per 100 fields) | Low bacterial load — repeat testing or culture recommended |
| 1+ (10–99 AFB per 100 fields) | Positive — consistent with active TB |
| 2+ (1–10 AFB per field) | Moderately positive — active TB with significant bacterial load |
| 3+ (Above 10 AFB per field) | Strongly positive — high bacterial load, highly infectious |
A negative AFB smear does not rule out TB — sensitivity is approximately 50–80%. TB culture and GeneXpert (molecular test) are more sensitive and are recommended when smear is negative but clinical suspicion remains high.
How to Prepare for the Sputum AFB Test
- Three sputum samples are typically collected on two consecutive days — two early morning samples (which are most concentrated) and one spot sample
- Collect sputum from deep in the lungs by taking a deep breath and coughing forcefully — saliva alone is not an adequate sample
- Collect the sample into the sterile container provided by the lab, preferably outdoors or in a well-ventilated area to prevent spreading infection
- Do not eat, drink, or use mouthwash before collecting an early morning sample
- Deliver the sample to the lab within 1–2 hours of collection, or refrigerate if delayed
Sputum AFB Test Price in Bangladesh
Sputum AFB test prices vary between diagnostic centers across Bangladesh. Compare sputum AFB test prices on MedTestBD →
Normal ranges cited on this page are based on MedlinePlus and WHO guidance. Prices are collected from public sources and may change — confirm with the facility before visiting. This information is for general reference only and is not medical advice. Always consult a qualified physician.
