Acid-Fast Bacilli (AFB) Smear and Culture

A-Z Navigation

A - Z Index:   A   B   C   D   E   F   G   H   I   K   L   M   N   O   P   Q   R   S   T   V   W   X   Y

 

Brief Description

Acid- Fast Bacilli (AFB) smear and culture are two separate tests always performed together at the MSPHL, Tuberculosis (TB) Unit.  AFB smear refers to the microscopic examination of a fluorochrome stain of a clinical specimen.  The AFB culture is the inoculation of a clinical specimen onto culture media Becton-Dickinson Mycobacteria Growth Indicator Tube (B-D MGIT broth) and Lowenstein-Jensen (L-J) media slant, incubation at 37°C for up to six (6) weeks and detection of growth or no growth during this incubation period.

Laboratory Unit

Tuberculosis

Methodology

AFB smear – fluorochrome staining

AFB culture – B-D MGIT system and conventional culture media.

Specimen Collection

Sputum:
  • An early morning, deep cough specimen collected on three (3) consecutive days is best for initial diagnosis of tuberculosis
  • If sputa are collected within the same 24-hour period, a minimum of eight (8) hours between specimens is required
  • Minimum acceptable specimen volume is two (2) mL
  • Ship specimens each day collected to facilitate rapid diagnosis; do not hold until three (3) specimens are collected
  • Refrigerate until shipped
Bronchial Washing:
  • Preferred minimum acceptable volume is two (2) mL
  • Refrigerate until shipped
Pleural Fluid:
  • Preferred minimum volume is two (2) mL
  • Refrigerate until shipped
Lung Tissue:
  • Add 1-2 mL of sterile normal saline for transport
  • Do not send tissue wrapped in gauze or paper
  • Refrigerate until shipped

Storage/Transport

Submit clinical specimens using the TB Category B carrier provided by the MSPHL in accordance with the Infectious Substance, Category B shipping guidelines.

Acceptable Specimen
Type(s)

Sputum
Bronchial Washing
Pleural Fluid
Lung Tissue

Test Request Form(s)

Tuberculosis Test Request Form

Possible Results

AFB Smear: 
1+ (Rare)
2+ (Few)
3+ (Moderate)
4+ (Many)
AFB Not Found
Smear Not Performed

AFB Culture:
Identification of Mycobacteria specie
No growth of Mycobacteria after 6 weeks
Unsatisfactory

Reference Range

N/A

Unacceptable Conditions

No identification on the specimen container or the container and request form identification do not match.

Clinical specimen received greater than seven (7) days from collection.

Specimen leaking on arrival.

Insufficient specimen volume (less than 2 mL).

When unsatisfactory specimen is obtained by noninvasive means (sputum), the specimen is discarded and the submitter is notified to submit a new specimen and request form.

When unsatisfactory specimen is obtained by invasive procedures, the specimen is held until consultation with the physician is made about processing an unsatisfactory specimen.

Interfering Substances

Tissue samples submitted in formalin.

Result Reported

AFB smears are reported within 24 hours of receipt; AFB cultures are reported: (1) at 6 weeks when no growth occurs or (2) when growth occurs and identification is made. 

All reports are faxed.

Fees

$48 charge – Private healthcare submitters

CPT Codes

N/A

LOINC/SNOMED Codes

AFB Smear:  676-7

AFB Culture:  543-9

Additional Information

N/A