AFB Smear and Culture

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Latest Edit: Hector 2014-03-21 (EDT)

See Also Lab Tests

The AFB Smear and Culture test is done to help detect and indentify a mycobacterial infection, to diagnosis tuberculosis and to monitor the effectiveness of treatment.[1], [2]


  • This test may be indicated in cases of a chronic cough, weight loss, fever, chills and weakness in order to determine if the symptoms are due to tuberculosis or another mycobacterial infection.
  • Indicated after a positive TB screening tests, especially if you are in a high-risk group for progressing to active disease.
  • Acid-fast bacilli (AFB) are a group of rod-shaped bacteria, the most common one belonging to the genus Mycobacterium.

Patient Preparation

  • For suspected cases of tuberculosis lung infections, three sputum samples are collected early in the morning on different days.
  • A bronchoscope may be used to collect fluid for those unable to produce sputum.
  • In children, gastric washings/aspirates may be collected.
  • Depending on symptoms, urine, or aspirate from the site of suspected infection, cerebrospinal fluid (CSF), other body fluids, or biopsied tissue samples may be submitted for AFB smear and culture.

Clinical Implications

Negative Smear:

  • Indicates that no infection is present.

Positive Smear:

  • Indicates a probable mycobacterial infection. A culture is required to confirm a positive diagnosis.

Associated Tests

  • TB Screening Tests, Bacterial Wound Culture, Susceptibility Testing, Mycobacteria tuberculosis nucleic acid amplification test, TB NAAT, Body Fluid Analysis, Sputum Culture, Adenosine Deaminase.


  1. Pagana Kathleen D, Pagana Timothy J (2006) Mosby's Manual of Diagnostic and Laboratory Tests, Mosby.
  2. Weatherby Dicken, Ferguson Scott (2002) Blood Chemistry and CBC Analysis: Clinical Laboratory Testing from a Functional Perspective, Bear Mountain.