MYCOBACTERIA (ACID-FAST BACILLI [AFB]), CULTURE, BONE MARROW
Test Code: AFBM
AFB bone marrow cultures may be submitted for patients suspected of disseminated Mycobacterial infections.
Disseminated/miliary tuberculosis is associated with immune-deficiency; patients who are co-infected with HIV, particularly those with advanced disease, are more likely to have positive blood cultures with M. tuberculosis.
Disseminated Mycobacterium avium complex may occur in patients with advanced HIV infection and is usually diagnosed with blood cultures; however, in symptomatic patients with two negative blood cultures, bone marrow cultures may be indicated.
Shared Health Testing Process: LJ slants and AFB Blood culture bottles (BACTEC Myco/F Lytic Vials) are available at the Bone Marrow bench or may be requested from the Mycobacteriology laboratory. Please contact the Microbiology laboratory or the Microbiologist-on-call if media is required.
Molecular detection (PCR/NAAT) of Mycobacteria from bone marrow is not available.
Bone marrow cultures are incubated up to 8 weeks. Any growth on the LJ slant or from the BACTEC Myco/F Lytic vials is evaluated by microscopy. AFB smear positives are reported immediately. Complete identification is performed from the LJ slants or subcultures of the BACTEC Myco/F Lytic vials.
The identification of M. tuberculosis, Mycobacterium avium complex and Mycobacterium gordonae is performed in-house. Other AFB-positive organisms are referred to the National Reference Centre for Mycobacteriology - National Microbiology Laboratory (NRCM-NML) for identification. Susceptibility testing for M. tuberculosis is performed routinely by the NRCM-NML. Susceptibility testing for non-tuberculosis mycobacteria may be requested by consultation with the Shared Health Microbiologist-on-call.
Patient Preparation Instructions:
Patients' sample collection should be conducted in accordance with Infection and Control Practices. The WRHA Acute Infection Prevention and Control Manual states that "when collecting specimens for suspected or active TB, specimens must be collected utilizing Airborne Precautions regardless of age".
Accurate patient identification must be made prior to sample collection. Patient identification should be done in accordance with site policy.
Samples and requisitions must be labeled/completed in accordance with the Shared Health Specimen Acceptance Policy.
Bone marrow collections are performed by the Haematologist as per the Shared Health Bone Marrow Collection - Aspirate and Biopsy Samples documents. 2-3 drops of bone marrow should be inoculated on an LJ slant. If there is sufficient bone marrow, 1 mL should be inoculated into a BACTEC Myco/F Lytic vial. Prior to inoculating the BACTEC Myco/F Lytic vial, the flip-off cap should be removed and the top of the bottle should be disinfected with 70% isopropyl alcohol (and allowed to dry for one minute).
LJ slant and TB Blood Culture Bottle (BACTEC Myco/F Lytic Vial) inoculated at the time of collection.
Bone Marrow: 1.0 mL
Pediatric Bone Marrow: 1.0 mL
Bone marrow for AFB cannot be collected in EDTA as even trace amounts inhibit the growth of mycobacteria.
Culture: No acid fast bacilli isolated after 8 weeks of incubation.
Weekdays (Monday - Friday). Mycobacteriology cultures are only performed at the Health Sciences Centre in Winnipeg. AFB positive cultures are phoned to the nursing unit immediately. Culture positive index cases of M. tuberculosis are phoned to the nursing unit immediately.
Transport immediately to the lab. Specimens should be stored at room temperature prior to transport.
Ensure samples that are being sent to a referral laboratory are packaged in accordance with Transport of Dangerous Goods recommendations for diagnostic samples.