Lab Information Manual

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.

AFB testing of joint fluid (native and prosthetic revisions) will only be performed if requested with appropriate clinical details (patients receiving immunosuppressive therapy, patients who failed to respond to antibacterial therapy, patients with recent intraarticular injections or a history of significant open joint trauma with chronic symptoms of infection and patients with risk factors for tuberculosis) or by microbiologist consult.

Recommendations:
The Canadian Tuberculosis Standards state that:
"Every effort should be made to obtain clinical samples for both mycobacteriologic (acid-fast bacilli smear, culture, nucleic acid amplification test) and histopathologic tests. If the specimen is insufficient for all testing, mycobacterial culture should be prioritized given it has the highest diagnostic yield and allows for gold-standard phenotypic drug testing.”
“Every person with presumed extra-pulmonary TB should also be assessed for pulmonary TB to assess infectiousness and potentially assist with diagnosis.”
“In general, tissue has a higher yield than liquid/biologic fluids."

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 and Mycobacterium spp. AFB smear negative samples require a microbiologist consult if a NAAT is required.
Susceptibility testing for M. tuberculosis is performed routinely by the NRCM-NML. Susceptibility testing for nontuberculous 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:

Preferred Device:

1 - Sterile Specimen Container (100 mL)

Sterile Specimen Container (100 mL)
Manufacturer:

Catalogue #:

Specimen Required:

Body fluids (excluding respiratory specimens, blood, bone marrow and urine)
As much as possible (10-15 mL recommended) (Adult and Pediatric)
CSF: As much as possible (2-3 mL minimum), up to 10 mL (Adult and Pediatric)

Referral:

Ensure samples that are being sent to a referral laboratory are packaged in accordance with Transport of Dangerous Goods recommendations for diagnostic samples.

Requisition:

_SH Microbiology - Provincial Requisition (R250-10-06)

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 and Negative for Mycobacterium spp. DNA.

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.