| Synonym(s): | NAAT for M. tuberculosis complex, TB NAAT, NAA |
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| Requisition Form | G-MYCO |
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| Test Description | Nucleic Acid Amplification Testing of clinical Specimens for detection of M. tuberculosis complex and rifampin resistance |
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| Pre-Approval Needed | For NAA testing of non-respiratory specimen types, please contact the Mycobacteriology Lab at 512-776-7342. |
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| Supplemental Information Required | N/A |
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| Supplemental Form(s) | N/A |
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| Performed on Specimens from (sources) | Respiratory specimens from human. |
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| Sample/Specimen Type for Testing | - sputum (unprocessed or processed sediment)
- bronchial washing (unprocessed or processed sediment)
- tracheal aspirates (unprocessed or processed sediment)
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| Minimum Volume/Size Required | 3 mL to 15 mL. |
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| Storage/Preservation Prior to Shipping | - Transport specimen as soon as possible.
- If transport is delayed over one hour, refrigerate specimen.
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| Transport Medium | - Do not use transport medium.
- A sterile, leak-proof, 50 mL conical tube preferred for primary container.
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| Specimen Labeling | - At least two patient identifiers are required on specimen (e.g., patient full name, date of birth, medical record number).
- Three patient identifiers are preferred.
- Patient identifiers on specimen label must exactly match identifiers on submission form. (e.g., abbreviated name on label and full name on form is not acceptable.)
- Additional DSHS Laboratory specimen labeling guidelines available online here.
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| Shipping and Specimen Handling Requirements | - Ship according to Dangerous Goods Regulations, IATA, and/or CFR 49
- Category B Biological Substance, UN3373 shipping requirements apply.
- Handle as infectious agent using universal precautions.
- Triple-contain in accordance with federal shipping regulations.
- Submitters are responsible for packaging and shipping specimens according to regulatory requirements.
- Laboratory does not supply collection kits or shipping materials.
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| Method | Cepheid GeneXpert PCR test amplifies and detects DNA of M. tuberculosis complex in clinical specimens and tests for mutations in the rpoB DNA region that can cause rifampin resistance. |
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| Turn-around Time | - 48 hours from specimen receipt in this laboratory.
- Positive reports and suspected rifampin resistance are communicated to the specimen submitter on day of testing.
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| Interferences/Limitations | - AFB Smear and Culture performed on processed specimens concurrently at DSHS Laboratory.
- A negative NAA test does not mean the patient does not have M. tuberculosis complex disease. Test results must be confirmed by culture of specimen for the presence of mycobacteria.
- If a processed specimen sediment is submitted for NAA only, the AFB culture must be in progress at the submitting laboratory site.
- Rifampin resistance must be confirmed by sequencing (such as MDDR testing at CDC) to rule out silent or neutral mutations.
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| Common Causes for Rejection | - Specimen leaked in transit.
- Missing identifier(s) on specimen container.
- No test requested on G-MYCO requisition form.
- Specimens received frozen, in formalin, or in culture medium will be rejected.
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| Additional Information | - There should be a high clinical suspicion of tuberculosis when ordering this test.
- NAA testing should be requested if the test results will make a difference to the patient’s treatment or if the test results will make a difference to the contact investigation.
- Patients should not have a laboratory diagnosis of tuberculosis disease already.
- Exception: If acquired rifampin resistance is suspected of a diagnosed tuberculosis patient, provider should seek a consult with TB Expert physicians who may request NAA testing to check rifampin status.
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