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  • Visualization of CBNAAT Test Results

    Content

    The test results of the Cartridge-based Nucleic Acid Amplification Test (CBNAAT) assay are displayed in the ‘View Results’ window, of the CBNAAT software.

     

    For visualizing the results after the test is completed:

    • In the CBNAAT Dx System window, click View Results on the menu bar.
    • The View Results window appears.
    • To select a test result, click View Test.
    • ‘Select Test to Be Viewed’ - dialog box appears.
    • Select the test of interest.
    • Click OK.

     

    Note: The selected test result appears in the ‘View Results’ window. A result will be displayed in PDF format. 

     

    To generate a PDF report

    • To generate a report in PDF format, click on “Report” and then select the result you want.
    • The PDF report will be generated.

     

    Interpretation of Test Results

    • The ‘View Results’ window displays information about the test, such as sample ID and run-time on the left-hand side panel.
    • The interpretation of the result is in the center, and the real-time PCR amplification curves are displayed at the bottom.   

     

    Figure: User 'View Results' Window showing the information about test, interpretation of results and real-time PCR curves

     

     

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  • CBNAAT Results Interpretation

    Content

    On completion of a test run, the Cartridge-based Nucleic Acid Amplification Test (CBNAAT) gives the following results:

    1. MTB DETECTED; Rif Resistance DETECTED
    2. MTB DETECTED; Rif Resistance NOT DETECTED
    3. MTB DETECTED; Rif Resistance INDETERMINATE
    4. MTB NOT DETECTED
    5. Error
    6. Invalid
    7. No result

    Conclusive results include: MTB NOT DETECTED, MTB DETECTED with Rif Resistance/ without Rif Resistance.

    Non-conclusive results include: MTB Detected, Rif Resistance Indeterminate, Errors, Invalid and No Result - the test has to be repeated in these cases.

     

    Figure: CBNAAT Result Algorithm

     

     

    Video : CBNAAT Results Interpretation

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  • CBNAAT Assay Limitations

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    The Cartridge-based Nucleic Acid Amplification Test (CBNAAT) test has some limitations such as:

    1. Bacterial load below the Limit of Detection (LOD ~ 130 CFU/ml) may result in a false-negative result.
    2. Patients on an anti-TB regimen can still have positive results due to killed bacilli in the specimen and hence cannot be used for follow-up.
    3. A positive test result does not necessarily indicate the presence of viable organisms. It is, however, presumptive for the presence of Mycobacterium tuberculosis (MTB) and Rifampicin (Rif) resistance.
    4. MTB detection is dependent on the number of organisms present in the sample. Quality specimen collection and timely processing of the sample will minimize the errors.
    5. Test results might be affected by anti-TB medication. Therefore, therapeutic success or failure cannot be assessed using this test, because DNA might persist following antimicrobial therapy.
    6. Mutations or polymorphisms in primer or probe binding regions may affect the detection of new or unknown MDR or Rif-resistant strains, resulting in a false-negative result.
    7. Any modification in sample processing may alter the performance of the test.
    8. Results should be interpreted in conjunction with clinical data available to the clinician.

    Video:  

    CBNAAT Assay Limitations

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  • Retest Procedure for CBNAAT

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    The assay needs to be repeated by using a new cartridge if one of the following test results occur:

    INVALID: An INVALID result indicates that Sample Processing Control (SPC) failed. The sample was not properly processed, or Polymerase Chain Reaction (PCR) was inhibited.

    ERROR: An ERROR indicates that Probe Check Control (PCC) failed, and the assay was aborted possibly due to the reaction chamber being filled improperly, a reagent probe integrity, syringe pressure issues, or failure of the CBNAAT module.

    NO RESULT: A NO RESULT indicates that insufficient data were collected. For example, the operator stopped a test that was in progress.

    RIF Indeterminate: RIF indeterminate result indicates that the sample has a less bacterial load.

    Program guidelines recommend obtaining a second specimen to confirm rifampicin resistance in these scenarios.

     

    How to Perform the Retest?

    • Leftover sputum or fresh sputum or reconstituted sediment: 

    Treat it with a new Sample Reagent (SR) and load it into the new CBNAAT cartridge.

    • Sufficient leftover SR-treated sample: 

    Use within 4 hours of initial addition of SR to the sample - Load into the new CBNAAT cartridge.

    Do not use SR-treated sample if it is more than 4 hours old - Over-treatment may lead to false-positive test results.

    Always use a new cartridge! 

    Video : Retest Protocol for CBNAAT

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