Sputum Test for TB (AFB and NAAT)
A test of phlegm coughed up from the lungs to look for TB bacteria and other infections.
Quick Summary
To diagnose lung TB and some chest infections.
TB bacteria under the microscope (AFB) and TB DNA by rapid tests such as CBNAAT/TrueNat.
Collect an early-morning sample after rinsing your mouth with water.
Overview
Sputum testing for TB is free at government health centres in India.
Rapid molecular tests also show resistance to rifampicin.
What It Measures
AFB smear
TB bacteria seen under the microscope.
NAAT
TB DNA and drug resistance.
How It's Performed
- 01
Rinse
Rinse your mouth with water, not mouthwash.
- 02
Cough deeply
Bring up phlegm from deep in the chest, not saliva.
- 03
Collect
Spit into the container and close it.
Interpreting Results & Next Steps
Discuss with Doctor
A negative result may need repeating if symptoms continue. Your doctor will explain what your result means and what happens next.
If values are High:
A positive result confirms TB; treatment starts promptly.
Sources and further reading
Last updated 21 October 2026. For more detail, see these trusted health organisations.
- Acid-Fast Bacillus (AFB) Tests(opens in a new tab) · MedlinePlus, US National Library of Medicine
- Sputum culture(opens in a new tab) · MedlinePlus, US National Library of Medicine