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Troubleshooting Non-interpretable DST

 

MGIT DST results should be available within 4-13 days (SIRE and other second-line drugs) or 4-21 days (PZA) if the standard procedure is followed. However, under certain conditions, the Instrument takes too long to read the tubes, and the results are reported uninterpreted. The reasons for these non-interpretable results, along with the suggested corrective action, are listed below:

 

Reason 

Suggested corrective action

Initial inoculum too light

  • Precise pipettes must be used for dilutions and addition to tubes.

  • If working with solid media, ensure that the media is not picked up during inoculum preparation. This interferes with reading 0.5 McFarland.

Initial culture too old

Ensure that the cultures selected for DST are in proper growth phase.
Initial inoculum too heavy Day 3-5 growth from MGIT tube to be diluted; if working from solid media, allow tube to settle and adjust suspension; Avoid clumps in suspension.
GC suspension for SIRE and PZA are different (1:00 vs 1:10) Prepare suspension carefully.

 

 

Resources: 

Mycobacteriology Laboratory Manual. 

 

Assessment

 

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Answer 4

 

 

Correct answer​

 

 

Correct explanation​

 

 

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Part of Pre-test​

 

 

Part of Post-test​

 

 
MGIT DST for first and second-line drugs should be available in how many days? 3 days 7 days  4-13 days 21 days  3 MGIT DST results should be available within 4-13 days (SIRE and other second-line drugs) or 4-21 days (PZA) if the standard procedure is followed.

 

YES

 

 

YES

 

 
                   


 

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