PHO laboratory testing update: Molecular detection of Mycobacterium tuberculosis complex and Rifampin/Isoniazid resistance
Please be aware that as of July 8, 2024, Public Health Ontario’s (PHO’s) Laboratory will be implementing the use of a multiplex, qualitative real-time PCR test (BD MAX MDR-TB assay) for the simultaneous detection of Mycobacterium tuberculosis complex (MTBC) and Rifampin (RIF) and Isoniazid (INH) resistance.
With the implementation of this test, the real-time PCR for detection of MTBC and Mycobacterium avium complex (MAC) test will be discontinued, and molecular detection of MAC will no longer be available. Testing of acid-fast bacilli (AFB) smear positive specimens with the line probe assay for detection of RIF and INH resistance (Hain GenoType MTBDRplus test) will be discontinued. This assay expands the scope of specimen types that can be tested to include non-respiratory and formalin-fixed, paraffin-embedded (FFPE) tissue in addition to respiratory specimens.
Important notes for Health Care Providers:
- This test will be performed on specimens submitted for mycobacteria culture if:
- It is from a new, untreated patient and the specimen submitted is AFB smear positive.
- The patient has no history of AFB positive cultures for the past three years and current submitted specimen is AFB smear positive.
- This test will NOT be performed on specimens submitted for mycobacteria culture that are AFB smear negative.
- Providers must request approval for PCR testing on AFB smear negative specimens by contacting the Microbiologist, the Operational Lead, or PHO’s Customer Service Centre within 72 hours of the date and time the specimen was received at PHO’s laboratory to ensure specimen integrity. Requests written on the requisition will not be accepted unless prior approval is obtained.
- This test targets DNA from viable and non-viable bacteria and cannot be used to monitor the progression or success of treatment of patients with anti-tuberculosis therapy, or whether a patient may be infectious. All molecular test results must be interpreted with caution and confirmed by culture and phenotypic drug susceptibility testing (pDST).
- Due to differences in sensitivity among the targets used for the detection of MTBC DNA and rifampin and isoniazid resistance mutations, recollection of specimens for the purpose of molecular detection of resistance is NOT recommended and should be determined by culture and pDST.
- The absence of RIF and INH resistance detection does not exclude the possibility of other contributory mechanisms of resistance.
- Testing will be performed daily, Monday to Friday (excluding holidays) at PHO’s Toronto laboratory. Turnaround time (TAT) for fresh specimens is up to four days from receipt at PHO’s laboratory. TAT for FFPE samples may take up to 10 days from receipt at PHO’s laboratory.
Additional information about this test can be found on the Mycobacterium – MTBC and Rifampin/Isoniazid Resistance PCR test information webpage.
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