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Troubleshooting False Susceptible DST Results
Learning Objectivesmention reasons and troubleshooting
Troubleshooting False Susceptible DST Results
The common reasons for getting false susceptible DST results, along with their corrective actions, are given in the table below:
Reason |
Corrective action |
Inoculum too light |
|
Suspension not homogeneous |
Ensure that the starting suspension is uniformly homogenized. |
Culture too old |
Ensure that the cultures selected for DST are in the proper growth phase. |
Growth control grew too fast |
Ensure that proper dilutions are used for inoculating the growth control tube. |
Proper amount of supplement the not added to the tubes |
Ensure that correct amount of supplement (as per the standard protocol) is added to the tubes. |
Supplement not stored properly |
Ensure that the supplement is stored as per the manufacturer’s instructions. |
Drugs not reconstituted properly |
Ensure that the lyophilized drugs are reconstituted as per the manufacturer’s instructions.the |
Too much drug added to tubes |
Ensure that exact volume (100 µl) of the drug is added to the tube. |
Incorrect media and/or supplement used for PZA |
Ensure that PZA medium and PZA supplement is used for PZA DST. |
Organism could be borderline-resistant |
Check the Growth units and repeat DST if GU is >95 but <100. |
Resources
GLI Practical Guide to TB Laboratory Strengthening
Assessment
Question |
Answer 1 |
Answer 2 |
Answer 3 |
Answer 4 |
Correct answer |
Correct explanation |
Page id |
Part of Pre-test |
Part of Post-test |
In the case of solid media, the initial suspension to be used for DST must satisfy which of the following conditions? |
> 1.0 McFarland |
> 2.0 McFarland |
<1.0 McFarland |
None of the above |
1 |
Ensure that the starting suspension is > 1.0 McFarland (in case of solid media). |
|
YES |
YES |
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