Interpretation of FL-LPA: Predicting Drug-resistance in Special Cases

Predicting Drug Resistance in Special Cases

1. When specimen tested contains a hetero resistant strain:
   • Mutated as well as a wild-type sequence can be detected
   • One of the mutation probes as well as corresponding wild type probe may stain positive on the respective strip
   • Whether the respective resistance becomes phenotypically evident, depends on the ratio of mutated and nonmutated sequences
2. The tested specimen contains more than one M. tuberculosis complex strain (due to mixed culture or contamination):
   • One of these strains harbors a mutation, one of the mutation probes as well as the corresponding wild type probe may stain positive.
   • Whether the respective resistance becomes phenotypically evident, depends on the ratio of the resistant and sensitive strain
3. Due to mixed infection with M. tuberculosis complex strain and a nontuberculous mycobacterium:
   • The TUB band may be missing
   • If resistance pattern develops, presence of M. Tuberculosis complex must be suspected and repeat test
4. All bands of a gene locus (including the Locus Control band) missing completely on a test strip:
   • DNA concentration below the limit of detection or indicates the presence of interfering substances
   • Repeat test
   • If cultivated sample generates result with complete katG locus missing
     • Indicates Isoniazid resistance

Resources

• GenoType MTBDR plus ver 2.0 kit, Instructions for Use.​
• GLI Line Probe Assays for Drug-resistant Tuberculosis Detection.

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