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microbial diseases laboratory

Test Name

Mycobacterium tuberculosis Complex (MTBC): Drug Susceptibility Testing, First-Line

Test Methodology

Phenotypic drug susceptibility testing of Mycobacterium tuberculosis complex at critical concentrations by BACTEC MGIT 960 system. 

Routinely tested drugs: isoniazid (INH) 0.1 Ī¼g/ml, rifampin (RIF) 1.0 Āµg/ml, ethambutol (EMB) 5.0 Āµg/ml, and pyrazinamide (PZA) 100 Āµg/ml.

Reflex Testing Criteria

If resistance to INH, RIF, and/or EMB is detected, second-line drug susceptibility testing will be performed. In addition, if an isolate is resistant to INH at 0.1 Ī¼g/ml, susceptibility testing to INH at 0.4 Ī¼g/ml concentration will be performed.

Pre-Approval Required

None

Supplemental Information and Required Form(s)

Form LAB 444 (PDF) ā€œMycobacteriology-Drug Susceptibility Testing of MTBC (CA only)ā€

Instructions on completing this form.

Required Specimen/Sample Type(s)

Pure culture on solid or liquid media. Slants (LJ/ 7H10) or liquid cultures (MGIT broth) are preferable culture media for submission.

Minimum Volume Required

Viable growth should be present on subculture. 

1.0 mL minimum if broth culture is submitted.

Specimen Stability

Room Temp: up to 4 weeks
Refrigerated (2 ā€“ 8Ā°C): up to 6 months; isolate may be subcultured 
Frozen: Subculture prior to submission

Rejection Criteria

  • Samples with insufficient or conflicting labelling
  • Leaking samples
  • Isolates with no growth
  • Isolates that are nonviable
  • Mixed cultures
  • Specimen/sample types not meeting acceptance criteria

Storage/Transport Conditions

Grow isolate under appropriate conditions and verify purity prior to shipping. Isolates may be stored under refrigeration or ambient temperature prior to shipping.

Transport Medium, if applicable

Not applicable

Specimen Labeling

Two identifiers, including patient full name, and at least one other identifier (specimen accession number, date of birth, medical record number).

Shipping Instructions and Specimen Handling Requirements

Ship isolates at ambient temperature or with cold packs; do not freeze. 

Follow the appropriate DOT/IATA approved shipping procedures. All the suspected MTBC human specimens should be shipped as a Biological Substance, Category B (UN3373). 

Suspected or confirmed MTBC cultures should be shipped as a Category A Infectious Substance, Affecting Humans (UN2814). 

Ensure that culture isolates are sent in media flask or tubes containing a screw-top cap that is additionally sealed with parafilm or tape for additional protection against leaking.  DO NOT send plate cultures.

Ship to: 

California Department of Public Health 
Microbial Diseases Laboratory 
ATTN: TB Drug Susceptibility Testing Unit 
850 Marina Bay Parkway, Specimen Receiving Room B106 
Richmond, CA 94804

Specimen Collection Instructions, if applicable

Not applicable

Turnaround Time

Average 2 weeks

Interferences & Limitations

Results may be delayed or rejected if mixed culture is submitted.

Reference Range

Not applicable

Additional Information

Isolates will be forwarded to CDC if further characterization is needed.

MDL Point of Contact

For questions regarding submissions, please email CDPHTBDST@cdph.ca.gov or call the MMPDS Section at (510) 412-3929

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