Download App iOS Android

AFB (SMEAR)

About the test
What is this test done for?
AFB (smear) or acid fast bacilli smear test is a specialized test done toevaluate presence of Mycobacterium tuberculosis in the given specimen. This specimen includes sputum, urine, tissue, or secretion.
Why is it Done?
This is a specialized test done for evaluating the presence of tuberculosis bacilli in the given specimen. Tuberculosis bacilli or Mycobacterium tuberculosis are also called as acid-fast bacilli, and presence of this bacillus in the given specimen indicates tuberculosis. Thus, this test is carried out to detect active tuberculosis infection in the patient. If this test is coupled with a sensitivity test, it helps in identifying the drug of choice for the treatment of tuberculosis.
When should it be performed?
This test is performed
  1. If a patient has symptoms of pulmonary tuberculosis
    • Cough lasting for >3 weeks
    • Cough that produces sputum, sometimes mixed with blood
    • Fever with chills
    • Weight loss (>10% total body weight)
    • Night sweats
    • Loss of appetite
    • Weakness and fatigue
    • Difficulty in breathing
  2. If a patient has symptoms associated with TB outside the lungs (extra-pulmonary). Symptoms depend upon the site of infection
    • Intestinal TB (IC TB)
      • Prolonged fever (>3 weeks)
      • Abdominal pain (colicky pain)
      • Vomiting
      • Unexplained weight loss
      • Previous history of TB of lungs
    • Renal TB (TB of kidneys)
      • Prolonged fever
      • Abdominal pain
      • Difficulty in passing urine
      • Unexplained weight loss
      • Previous history of TB of lungs
    • Bone TB
      • Easy fracture
      • Pus formation in the bone
      • Unexplained weight loss
      • Previous history of TB of lungs
    • TB of meninges (Tubercular meningitis)
      • Headache
      • Neck tightness
      • Fever
      • Delirium
      • Unexplained weight loss
      • Vomiting
      • Previous history of TB of lungs or exposure to TB bacilli
  3. If a patient has been immunocompromised (affected with HIV infection or ADIS) and is exposed to a person who has TB or is in close contact with TB patient
  4. If a patient has a history of TB, and he has discontinued the treatment in between and is presenting with symptoms of TB
  5. If a patient had been treated for TB, this test is carried out to evaluate the effectiveness of the treatment
How is it done
In case of patient having cough with sputum, an early morning sputum sample is collected in a clean sterile container. Before collecting the sample, you must rinse your mouth with plain water. In case a patient has symptoms of TB outside lungs, the tissue sample is collected in a clean sterile container.
Results
The test result is negative, if no growth is seen in 48 hours. It indicates the absence of the mycobacterial infection. The test result is positive, if growth of acid-fast bacilli is seen. It indicates the presence of the mycobacterial infection. After a positive growth, slides are prepared from that growth and studied under the microscope using acid-fast stain. Further, this culture growth is exposed to various antibiotics and zone of inhibition is noted. A complete zone of inhibition with a specific antibiotic suggests that the antibiotic used is the drug of choice for the mycobacterial infection
Other Tests
  • Sputum culture
    • Positive growth suggests the presence of pathogenic bacteria
  • Mantoux test
    • Positive test indicate either ongoing TB infection or previous exposure to the TB bacilli
  • Blood culture
    • It is a specialized blood test carried out to check the infection present in the blood and bacteria or fungus responsible for it
    • Presence of Mycobacterium indicates TB
100%
Trusted Labs
Upto 75%
off on diagnostic tests
Free sample pickup