Laboratory: Clinical Microbiology
Test Name:
Test Code: AFBB
Clinical Information:
Test Indications:
AFB blood cultures are indicated for patients suspected of disseminated mycobacterial infections.
Disseminated nontuberculous mycobacteria (NTM) disease may occur in patients with advanced HIV infection.  Specifically, patients with HIV and CD4+ T cells counts of <50 CD4+ T cells/uL are at risk of disseminated NTM disease.
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.

Shared Health Testing Process - All diagnostic testing for mycobacteria is performed in the Mycobacteriology Section of the HSC Clinical Microbiology Laboratory.
AFB blood culture bottles (BACTEC Myco/F Lytic Vials) are available directly from the Mycobacteriology Section of the HSC Clinical Microbiology Laboratory.  Please contact the HSC Clinical Microbiology Laboratory or the HSC Shared Health Microbiologist-on-call if an AFB blood culture bottle is required.
Molecular detection (PCR/NAAT) of mycobacteria from blood cultures is not available.
The inoculated BACTEC Myco/F Lytic vials are incubated on the blood culture instrument in the Mycobacteriology Section of the Clinical Microbiology Laboratory for up to 42 days (6 weeks).  When a positive vial is detected, it is evaluated by microscopy and subcultures are performed.  AFB smear positives are reported immediately.  Complete identification is performed from the subcultures.
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 HSC Shared Health Microbiologist-on-call.

Patient Preparation Instructions:
Patients' sample collection should be conducted in accordance with Infection Prevention 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 patient 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.
The venipuncture site should be cleansed as per the Shared Health Phlebotomy Collection Manual.  Briefly, remove the flip-off cap from the bottle, disinfect the top of the bottle using 70% isopropyl alcohol, and wait one minute for it to dry.  Using a chlorhexidine/70% alcohol swab, use a back and forth friction rub motion to cleanse the selected venipuncture site, using sufficient pressures so that the shaft of the swab bends slightly.  Cleanse with one side of the swab for 15 seconds covering a 4 x 4 cm area.  Turn the swab over and cleanse the area using a back and forth friction rub in the opposite direction.  Let the area dry for 20 seconds.  Without re-palpating the vein, perform the venipuncture. 
Inoculate the AFB blood culture bottle with 1-5 mL of blood.
Collection Devices:
Specimen Required:
Blood: 5.0 mL
Pediatric Blood: 5.0 mL

Blood for AFB cannot be collected in EDTA as even trace amounts inhibit the growth of mycobacteria.  Coagulated blood, serum and plasma are also unacceptable.
Reference Values:
Culture: No acid fast bacilli isolated after 6 weeks of incubation.
Weekdays (Monday-Friday). Mycobacteriology cultures are only performed at the HSC Clinical Microbiology Laboratory in Winnipeg. AFB positive blood cultures are phoned to the nursing unit immediately.
See Also:
More Information:
Specimen Handling:
Transport immediately to the laboratory.  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.