Mycobacterium – PCR for MTBC/MAC
Consistent with O. Reg. 671/92 of the French Language Services Act, laboratory testing information on this page is only available in English because it is scientific or technical in nature and is for use only by qualified health care providers and not by members of the public.
Specimen Requirements
| Test Requested | Required Requisition(s) | Specimen Type | Minimum Volume | Collection Kit |
Mycobacterium PCR for MTBC/MAC |
Fresh specimens |
5.0 ml |
||
Mycobacterium PCR for MTBC/MAC |
Concentrate |
0.5 ml |
||
Mycobacterium PCR for MTBC/MAC |
Formalin Fixed Tissue or Formalin Fixed Paraffin Embedded (FFPE) block and H & E stained slide |
N/A |
Submission and Collection Notes
Collect fresh specimens using aseptic technique in sterile containers without fixative. Frozen specimens will not be tested.
Acid-fast bacilli (AFB) smear-negative specimens will be tested only upon request and must be requested within 72 hours of the date and time the specimen was received to ensure specimen integrity. Requests should be considered for patients in whom tuberculosis is highly likely and have significant risk factors for tuberculosis. A negative result cannot be used to “rule out” tuberculosis. The physician must phone the Medical Microbiologist or the lab Operational Lead for approval to request the real time PCR assay.
Contact Public Health laboratory prior to submission of FFPE. FFPE specimens should only be submitted when there is a strong suspicion of tuberculosis disease clinically and epidemiologically, and there is evidence observed on histopathological examination of the tissue (e.g. caseating granulomata visualized on histopathology or acid-fast organisms seen on ZN staining). This information should be part of the histopathology report. Please note that the Real time PCR assay cannot be used as a “rule out” test. FFPE samples submitted without prior notice to the laboratory and without the information required as indicated above will not be tested, and will be returned to the submitting laboratory. Fresh tissue is the specimen of choice, FFPE should only be submitted if fresh tissue is not available.
The paraffin block and slide will be returned to the submitter after testing has been completed. A core biopsy may be used in its entirety for TB PCR. Please identify TB as priority.
Since mycobacterial organisms are distributed unevenly in tissues, for FFPE samples indicate on the slide the suspect areas (e.g. granulomatous inflammation, caseating granulomata, organisms visualized by ZN etc.) in order to improve the potential for molecular detection of M. tuberculosis complex DNA.
Timing of Specimen Collection
Fresh specimens, or the treated concentrate from a fresh specimen (concentrate must be tested within 72 hours of treatment to maintain sample integrity)
Limitations
Tests performed on smear negative samples do not “rule out” when target DNA is not detected.
Nucleic acid amplification tests, such as this real time PCR assay, target nucleic acids from viable and non-viable bacteria, and cannot be used to monitor the progression or success of treatment of patients with anti-tuberculous therapy, or whether a patient may be infectious.
Results are qualitative (i.e., “detected” or “not detected”) and cannot be used to determine bacillary load.
This real time PCR assay contains an internal inhibition control. In the presence of inhibiting factors, an indeterminate result will specify that it is due to inhibition within the sample. The assay has a slightly lower sensitivity for detecting M. avium complex organisms, particularly with mixed cultures.
Storage and Transport
Label the container with two identifiers and place specimen in a biohazard bag and seal. Store fresh samples or concentrates at 2-8 °C if transport is delayed more than one hour. Specimens should be transferred to the lab ASAP.
Place specimen container(s) in the biohazard bag and seal bag, and insert the completed requisition in the pocket on the outside of the sealed biohazard bag.
Special Instructions
Store fresh samples or concentrates at 2-8 °C if transport is delayed more than one hour. Specimens should be transferred to the lab ASAP.
Test Frequency and Turnaround Time (TAT)
Real time PCR for the detection of MTBC and MAC is performed daily, Monday to Friday (excluding holidays).
TAT for fresh samples is up to 4 days from receipt by PHO Laboratory. TAT for FFPE samples may take up to 10 business days.
Real time PCR for detection of Mycobacterium tuberculosis Complex (MTBC) and Mycobacterium avium Complex (MAC) DNA is performed on all AFB smear positive specimens from new, untreated patients. Repeat testing is done on AFB smear positive specimens from patients who have had no AFB positive cultures for the past three years. A patient with a treated and resolved past history of tuberculosis may give a positive test for several years post treatment and/or may give a negative result after a short period of patient treatment. PCR testing, which only detects the presence of certain DNA sequences and not necessarily viable organism, is used to find new cases of MtbC and cannot be used to follow treatment or disease progression. Interpretation of NAAT test results beyond this purpose have not been validated.
For requests for testing on AFB smear negative specimens, when there is a strong clinical suspicion of TB, the physician must phone the Medical Microbiologist or the lab Operational Lead for approval. Requests written on the requisition will not be accepted unless prior approval is obtained.
FFPE samples are also tested for the presence of MTBC and MAC DNA. The possibility of environmental contamination of these samples, particularly by non tuberculous mycobacteria, means that any result should be considered within the overall clinical picture.
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