MYCOBACTERIA (ACID-FAST BACILLI [AFB]), CULTURE, URINE
Test Code: AFBF
Urine for AFB testing may be submitted for patients suspected of genitourinary tuberculosis. Urine AFB specimens should not be submitted for a routine screen; samples should only be submitted if renal or urinary tract tuberculosis is suspected.
The Canadian Tuberculosis Standards recommend that:
First-void morning urine should be submitted - 1 per day for 3 days.
The patients should be off fluoroquinolones, which may have been prescribed for a superimposed bacterial infection, for 48 hours prior to sample collection for AFB. The fluoroquinolones may affect the mycobacteria and reduce the culture yield.
Shared Health Testing Process - Every AFB urine 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 urine 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. Please indicate on the requisition if the patient has received intravesical Bacillus Calmette-Guerin therapy.
Patient instructions for the collection of urine are available in Shared Health doc# PB120-10-05B.
1 - Sterile Specimen Container (100 mL)
40 mL of midstream urine or catheter urine, (minimum of 10-15 mL) (Adult and Pediatric)
For suprapubic taps, as much specimen as possible.
Do not pool urine samples. Do not add preservatives or additives.
For suprapubic taps, aspirate should be submitted in a sterile container. Do not submit samples in a syringe with the needle attached.
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.