Acid Fast Bacilli (AFB) (Staining, Smear & culture sensitivity) - Sputum

Clinical definition of the Acid Fast Bacilli Culture test
An acid-fast Bacillus (AFB) culture refers to the process of detection, growth, isolation, identification, and antibiotic susceptibility testing of Mycobacteria that cause pulmonary tuberculosis and other infections such as those of the skin, abdomen, and may widely spread throughout many organs. It has become important in the identification of other acid-fast AFB such as Mycobacterium tuberculosis and M. leprae, M. avium complex (MAC), M. bovis, and M. africanum. Tuberculosis usually attacks the lungs but can also affect other parts of the body. It is spread through the air when people who have the disease cough, sneeze, or spit. The other widely used tests used in the diagnosis & screening of Tuberculosis infection are:

  • AFB, smear examination
  • Culture, Mycobacterium Tuberculosis
  • Mantoux test (Tuberculin skin test)
  • Mycobacterium antibody panel (TB-IgG, IgM, IgA)
  • Mycobacterium Tuberculosis by RT-PCR
  • Quantiferon TB Gold

Why is the Acid Fast Bacilli Culture test done?
This test uses a microscope for routine health screenings, to detect the acid-fast bacilli in sputum, fluid or tissue samples and to manage the medication of mycobacterial infections such as tuberculosis. It may also be used when an atypical mycobacterial infection is suspected.

What are the common signs/symptoms when the Acid Fast Bacilli Culture test is done?
These symptoms may be diagnosed by, screened for, or associated with Acid-fast bacilli smear:

  • Unexplained weight loss
  • Fatigue
  • Fever
  • Night sweats
  • Chills
  • Loss of appetite
  • Prolonged and Persistent cough
  • Blood in sputum
  • Painful breathing
  • Painful coughing
  • When TB severely spreads in the lungs it shows the following symptoms include 
  • Chest pain, 
  • Coughing up blood
  • Prolonged cough for more than three weeks

Who should do the Acid Fast Bacilli Culture test (Target population)?
Persons showing the above signs & symptoms.

What should I do before the Acid Fast Bacilli Culture test?

Specimen type

Specimen collection procedure

Preparatory instructions before the test *


The mouth should be free of any foreign matter. If available, the mouth may be rinsed with filtered or sterile water prior to collection.

Instruct the patient to inhale deeply 2-3 times, cough up deeply from the chest and spit in the sputum container by bringing it closer to the mouth.

A good sputum sample is thick, purulent and sufficient in amount (at least 2-3 ml).

No other special preparations required

A sample of sputum, bronchial samples, blood, cerebrospinal fluid, urine, stool, or other body fluids or tissues may be collected for this test.

*Subjects suffering from any illness or on oral or injectable medications are advised to consult their physician prior to requesting any tests or procedures.

How do I interpret my Acid Fast Bacilli Culture test results?

Reference Range*


+ or ++

Positive for Mycobacterium spp.


Negative for Mycobacterium spp.

Inference- The number of positive bacilli varies, depending on the severity of infection.
‘*A Reference range is a set of values which helps the healthcare professional to interpret a medical test. It may vary with age, gender, and other factors. Reference ranges may also vary between labs, in value & units depending on instruments used and method of establishment of reference ranges’

Diseases/conditions related to the Acid Fast Bacilli Culture test

  • Tuberculosis

Other tests related to the Acid Fast Bacilli Culture test

  • Acid Fast Baciili Culture Test
  • Mantoux Test
  • Anti TB
  • TB-PCR Test
  • Quantiferon TB Gold Test
  • Molecular testing, diagnostic
  • Atypical mycobacterial infection
  • TB skin test
  • Bacterial wound culture

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AFB Smear (Sputum)