Laboratory: Clinical Microbiology
Test Name:
MYCOBACTERIA (ACID-FAST BACILLI [AFB]), CULTURE, RESPIRATORY (Sputum/Bronchial Alveolar Lavage (BAL)/Bronchial Washings)
Test Code: AFBR
Clinical Information:
Testing Indications:
Respiratory specimens submitted for acid-fast bacilli (AFB) detection are processed for the identification of Mycobacteria species [Mycobacterium tuberculosis and nontuberculous mycobacteria (NTM)].
The Canadian Tuberculosis Standards state that "testing for active tuberculosis (TB) is indicated in everyone with signs and symptoms of TB or considered to be at high risk for TB.
Sputum specimens for AFB detection are one of the minimum evaluation criteria for patients suspected of nontuberculous mycobacteria.

For the initial diagnostic samples of tuberculosis, at least three sputum samples of 5-10 mL (min. 3 mL) should be collected and submitted for testing by microscopy and culture, prior to the commencement of therapy.  The samples may be collected on the same day, at least 1 hour apart.
For follow-up samples of known tuberculosis-positive patients, three sputum samples of 5-10 mL (min. 3 mL) should be collected 8-24 hours apart (with 1 early morning sample preferred).  Follow-up samples should be submitted after two months of effective TB therapy to ensure the specimens are culture negative.
For nontuberculous mycobacteria, three early-morning sputum samples should be collected on separate days.
Induced sputum may be submitted when expectorated sputum cannot be collected.  Bronchoscopy samples (BAL, Bronchial wash/brush), Endotracheal aspirates, and Transtracheal aspirates can be collected when expectorated or induced sputum are unavailable.  5-10 mL (min. of 3 mL) of sample should be submitted.

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.
Expectorated Sputum Collection Guidelines: "How to Collect a Sputum Sample" PB120-10-05E (English and French)
Induced sputum should be collected as recommended by the Respiratory Therapy Departments.
1. Using a nebulizer, have the patient inhale a large volume (approximately 25 mL) of 3% hypertonic saline.  2. Collect the induced sputum in a sterile container.
Collection Devices:
Preferred Device:
Alternate Device:
1 - Sterile Aspiration Trap  - for Bronchial washings/aspirates
Bronchial brushes should be placed in a Sterile Specimen Container (100 mL) with up to 5 mL of saline.
Specimen Required: Sputum, BAL, Bronchial wash/brush, Endotracheal aspirate, Tracheal aspirate - 5-10 mL (minimum of 3 mL) (Adult and Pediatric)
Do not add preservatives or additives.  Do not pool sputum samples.

Ensure induced sputum samples are labelled as "induced sputums".  The induced specimens may appear watery but will be processed the same was as expectorated sputum samples when they are labelled accurately.
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.
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. STAT AFB testing is not available.
See Also:
More Information:
Specimen Handling:
Respiratory samples should be refrigerated for storage.
Samples may be held at room temperature for less than 2 hours.
Ensure samples that are being sent to a referral laboratory are packaged in accordance with Transport of Dangerous Goods recommendations for diagnostic samples.