AFB (TUBERCULOSIS) Sample Type: Sputum

This test checks for acid-fast bacilli (AFB) like Mycobacterium tuberculosis in sputum to diagnose pulmonary tuberculosis (TB). It's used when patients show symptoms like a persistent cough, weight loss, or night sweats. Sputum samples are usually collected over 3 days, preferably in the morning. A positive result suggests active, contagious TB, while a negative result doesn't rule it out and may require further testing like culture or molecular analysis.

By Allschoolabs · August 4, 2025 · 46 views

AFB (Tuberculosis) – Sputum Test
Sample Type: Sputum

Purpose:
This test detects acid-fast bacilli (AFB), primarily Mycobacterium tuberculosis, in a sputum sample. It is a key diagnostic tool for pulmonary tuberculosis (TB).

About AFB:
AFB are a group of bacteria, including Mycobacterium tuberculosis, that resist decolorization by acid-alcohol after being stained—hence the term "acid-fast." TB is transmitted through airborne droplets and mainly affects the lungs.

Indications for Testing:

Persistent cough lasting more than 2–3 weeks

Coughing up blood, chest pain, weight loss, night sweats

Suspected or known exposure to tuberculosis

Monitoring treatment effectiveness in TB patients

Sample Collection & Handling:

Early morning sputum samples (usually 3 consecutive days) are ideal.

The patient is instructed to cough deeply to produce a specimen from the lungs (not saliva).

Samples must be collected in a sterile container and transported promptly.

Diagnostic Methods:

Ziehl-Neelsen staining for microscopy

Fluorescent staining (e.g., auramine-rhodamine)

Culture for TB bacteria (more sensitive but takes longer)

Molecular tests (e.g., GeneXpert MTB/RIF) for rapid detection and rifampicin resistance

Clinical Significance:

Positive AFB smear: Likely active TB infection; patient is infectious

Negative smear: Does not rule out TB; further testing (culture or molecular) may be needed