TB Investigations
Investigations Microscopy for AFB

Culture and sensitivity of Mycobacteria species, including TB
Inform lab before sending No
Specimen type
  • Sputum & Bronchoalveolar lavage, (BAL's)
  • Urine
  • CSF
  • Blood and Bone Marrow
  • Body fluids /aspirates 5-20ml
  • Pus samples
  • Faeces
  • Gastric lavage
  • Laryngeal swabs
  • Skin/tissue/biopsies and Post mortem samples
  • Environmental Water specimens from heater cooler units
  • Ideal time to take specimen Before antimicrobial therapy where possible
    Labelling requirements click here
    How to take the specimen Sputum & Bronchoalveolar lavage, (BAL's) 5 ml or greater :
    3 fresh, purulent samples from the lower respiratory tract collected on consecutive days

    3 fresh early morning samples (EMU) collected on consecutive days (mid-stream EMU are acceptable but full EMU samples are preferable).

    CSF: 6ml (for adults) CSF in sterile leak proof container

    Blood and Bone Marrow specimens must be inoculated into a specialised Mycobacteria blood & bone marrow culture bottle (contact the Bacteriology laboratory for bottles). Where possible it is recommended that blood culture bottles are inoculated at the bedside.

    NOTE: If blood for other tests such as blood gases or ESR is to be taken at the same venepuncture, the blood culture bottles should be inoculated first to avoid contamination. It is preferable to take blood for culture separately, using aseptic technique, disinfect the skin at the venepuncture site using ethanol or isopropyl alcohol and allow to dry:

  • Check bottle expiry date before use and visually check for any signs of damage or contamination. A bottle should not be used if any signs of cracks or leakage are noted. The media should be a clear yellow colour, do not use any bottles where the media shows signs of turbidity.
  • Wipe the top of the bottle with an alcowipe, allow to air dry and inoculate the bottle with 1-5ml of blood or bone marrow. After inoculation disinfect the bottle cap with an alcowipe and allow to air dry.
  • Label bottle with patient information

    The following should be sent to the laboratory in a sterile leak proof container:

  • Body fluids /aspirates 5-20ml
  • Pus samples
  • Faeces
  • Gastric lavage
  • Laryngeal swabs
  • Skin/tissue/biopsies (add a few drops of sterile saline to prevent drying) and Post mortem samples
  • Biopsies should NOT be supplied in formalin
  • Environmental Water specimens from heater cooler units (minimum 100ml)
  • Transport to the laboratory Send samples to laboratory via porter. Only in exceptional circumstances should these blood cultures be drawn outside normal laboratory hours.

    Test Times Monday to Friday
    Turnround Direct microscopy for AFB
  • 24 hours (excluding weekends)
    Positive AFB smear to Direct MTB PCR result
  • 24 hours (excluding weekends)
    Positive AFB smear to Culture result
  • 1 - 3 weeks for MTB
  • 1 - 6 weeks for atypical mycobacteria
    Negative AFB smear to Culture result
  • Up to 6 weeks for MTB
  • Up to 10 weeks for atypical mycobacteria
  • Note: Positive cultures are routinely sent to reference laboratory for confirmation of identification and antibiotic sensitivity testing.
    Positive Culture to Gene Probe Identification
  • 4 days (excluding weekends)
    Positive Culture to full identification and antibiotic sensitivity result
  • 4 weeks
  • Additional information If transport is delayed then refrigerate sample (not blood/bone marrow culture bottles, store these at room temperature). Delays of over 48 hours are undesirable Microscopy and culture for AFB are NOT routinely performed on all sputum samples received and the need for this investigation should be clearly marked on the request
    Additional Examination Requests Please ensure that any requests for additional investigations on the specimen are made within 7 days from the date of the original request


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