MYCOBACTERIA (ACID-FAST BACILLI [AFB]), CULTURE, STOOL
Test Code: AFBP
Stool for AFB testing may be submitted for patients suspected of intestinal tuberculosis and HIV-positive patients who may also have gastrointestinal involvement with Mycobacterium avium complex.
The Canadian Tuberculosis Standards recommend that:
"It is important to assess for pulmonary involvement when considering the diagnosis of enteric TB, as up to 50% of patients with intestinal TB have evidence of active or inactive pulmonary TB on chest radiography."
Shared Health Testing Process - Every AFB stool sample is evaluated by microscopy and culture. Samples are decontaminated and concentrated prior to 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.
The nucleic acid amplification test (NAAT)/PCR is NOT validated for stool samples.
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.
Patient instructions for the collection of a stool sample are available in Shared Health doc# PB120-10-05D.
1 - Sterile Specimen Container (100 mL) - Rectal swabs will be rejected as inappropriate samples.
Feces : 2.0 g
Pediatric Feces : 2.0 g
1-2 grams (walnut size) of fresh stool. Do not add preservatives or additives.
Microscopy: No acid-fast bacilli observed.
Culture: No acid fast bacilli isolated after 7 weeks of incubation.
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.
Samples should be refrigerated for storage.
Ensure samples that are being sent to a referral laboratory are packaged in accordance with Transport of Dangerous Goods recommendations for diagnostic samples.