Laboratory: Clinical Microbiology
Test Name:
MYCOBACTERIA (ACID-FAST BACILLI [AFB]), CULTURE, FLUID
Test Code: AFBF
Clinical Information:
Test Indications:
AFB fluid samples may be submitted from 1) the affected body site for patients suspected of non-respiratory tuberculosis and 2) the affected body site for patients suspected of non-respiratory nontuberculous mycobacterial (NTM) disease.

Recommendations:
The Canadian Tuberculosis Standards recommend that:
"Whenever practical, every effort should be made to obtain clinical samples for both mycobacteriologic (AFB smear and culture) and histopathologic tests.  Drug susceptibility testing can only proceed with a viable culture…".   "In general, tissue biopsy yields positive culture results more often than fluid aspiration; both are superior to swabs".

Shared Health Testing Process - Every AFB fluid culture is evaluated by microscopy and culture.  Smears are reported semi-quantitatively (Negative or 1+ to 4+).  Cultures are incubated for 7 weeks and reported as soon as growth is detected.  All microscopy smear positive AFB samples receive nucleic acid amplification testing (NAAT).  The in-house NAAT detects M. tuberculosis (not all Mycobacteria).  AFB smear negative samples require a microbiologist consult if a NAAT is required.  For non-CSF fluids, the sensitivity of smear negative samples is reduced (75% compared to up to 100% for smear positive samples).  For CSF fluids, the clinical sensitivity and specificity have not been determined for the NAAT; however, the Canadian Tuberculosis Standards state that "A positive NAA assay result from the CSF of a patient with a high clinical probability of TB meningitis can be considered a presumptive cases, whereas a negative NAA assay in these circumstances cannot be relied upon to exclude the diagnosis."
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 nontuberculosis 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.
Collection Devices:
Specimen Required: Body fluids (excluding respiratory specimens, blood, bone marrow and urine)
As much as possible (10-15 mL minimum) (Adult and Pediatric)
CSF: As much as possible (2-3 mL minimum), up to 10 mL (Adult and Pediatric)
Referral:
Requisition:
Reference Values:
Microscopy:  No acid-fast bacilli observed.
Culture:  No acid fast bacilli isolated after 7 weeks of incubation.
NAAT:  Negative for Mycobacterium tuberculosis complex DNA by Real-time PCR.
Availability:
Weekdays
Weekdays (Monday - Friday). Mycobacteriology cultures are only performed at the Health Sciences Centre in Winnipeg. AFB positive smears of specimens are phoned to the nursing unit immediately. Culture positive index cases of M. tuberculosis are phoned to the nursing unit immediately. Positive M. tuberculosis NAAT results of index cases are phoned to the nursing unit immediately.
See Also:
More Information:
Specimen Handling:
Samples should be refrigerated for storage, except CSF, which should be at room temperature.
Ensure samples that are being sent to a referral laboratory are packaged in accordance with Transport of Dangerous Goods recommendations for diagnostic samples.