Validation of Resistant/Unexpected MGIT DST Results

Validation of Resistant/Unexpected MGIT DST Results

1. Validation of Resistant MGIT DST Results

Observe all ‘resistant’ tubes visually for evidence of contamination when first removed from the instrument. Then, perform a ZN stain on any suspicious tube and subculture to a Blood agar plate (BAP) or Brain Heart infusion (BHI) agar plate to rule out the contamination.

In addition, when drug resistance is observed, and the patient’s isolate has not been tested before, or if the isolate was not previously resistant to the drug, test the tube(s) with ZN and BAP/BHI to ensure that growth is not due to contaminants or Mycobacteria Other Than Tuberculosis (MOTT).

2. Validation of Unexpected MGIT DST Results

If DST results for any drug are inconsistent with previous results for the same patient, review the results and QC and repeat the test. If the repeat result is discrepant with the first result, repeat the test a third time and record the third test result as the tiebreaker.

Resources

1. Mycobacteriology Laboratory Manual

2. Revised National TB Control Programme Training Manual for Mycobacterium tuberculosis Culture & Drug susceptibility testing, Central TB Division, Ministry of Health and Family Welfare, GOI

Assessment