What is “Sputum for AFB”?

The Sputum for AFB (Acid-Fast Bacilli) test detects Mycobacterium tuberculosis — the bacteria that cause tuberculosis (TB).
It looks for AFB in mucus (sputum) coughed up from the lungs.

Why is it Done?

Doctors recommend this test to:

• Diagnose pulmonary TB.

• Confirm TB in patients with chronic cough, weight loss, fever, or night sweats.

• Monitor TB treatment progress.

How the Test Works

1. Sample Collection

   • Patient coughs deeply to bring up mucus from the lungs.

   • Collected in a sterile container.

   • Usually 3 samples are taken:

     • First spot sample – at the clinic.

     • Early morning sample – next day, before eating/drinking.

     • Second spot sample – when bringing the morning sample to the lab.

2. Laboratory Testing

   • Smear Microscopy – Stain the sputum with a special dye to see AFB under a microscope.

   • Culture – Grow the bacteria to confirm TB (more sensitive, takes weeks).

   • Molecular tests (GeneXpert) – Detect TB DNA and drug resistance quickly.

Preparation

• Collect before starting TB antibiotics (for accurate result).

• Rinse mouth with clean water before sample collection (remove food debris).

• Do not collect saliva — must be deep cough sputum.

Results

• Positive AFB → TB infection confirmed.

• Negative AFB → TB unlikely, but further tests may be needed if symptoms persist.

Quick Facts

• The AFB test is the gold standard for confirming TB.

• Early morning sputum is best — bacteria concentration is higher.

• In India, TB is notifiable, meaning positive results are reported to public health authorities for treatment follow-up.