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Test Code TB1LN Antimicrobial Susceptibility, Mycobacterium tuberculosis Complex, First Line, Varies

Infectious

Test Down Notes

Effective August 08, 2024:   This test is temporarily unavailable due to reagent supply.  The downtime is expected to be >30 days.  Order TB2LN as an alternative. See test notification here.


Ordering Guidance


If testing for the first-line agent pyrazinamide is desired, order TBPZA / Susceptibility, Mycobacterium tuberculosis Complex, Pyrazinamide, Varies.



Additional Testing Requirements


If organism identification is not provided, CTB / Mycobacteria and Nocardia Culture, Varies or CTBID / Culture Referred for Identification, Mycobacterium and Nocardia, Varies must also be ordered and will be charged separately.



Shipping Instructions


1. See Infectious Specimen Shipping Guidelines in Special Instructions.

2. Place specimen in a large infectious container (T146) and label as an etiologic agent/infectious substance.



Necessary Information


Specimen source and suspected organism identification are required.



Specimen Required


Specimen Type: Organism

Supplies: Infectious Container, Large (T146)

Container/Tube: Middlebrook 7H10 agar slant

Specimen Volume: Isolate

Collection Instructions: Organism must be in pure culture, actively growing.


Forms

If not ordering electronically, complete, print, and send a Microbiology Test Request (T244) with the specimen.

Useful For

Susceptibility testing of Mycobacterium tuberculosis complex isolates growing in pure culture.

Additional Tests

Test ID Reporting Name Available Separately Always Performed
STV1 Susceptibility, Mtb Complex, Broth No, (Bill Only) Yes

Reflex Tests

Test ID Reporting Name Available Separately Always Performed
TB2LN Susceptibility, Mtb Complex, 2 Line Yes No

Testing Algorithm

When this test is ordered, the additional test will always be performed and charged separately.

 

If resistance to a first line antimicrobial agent is detected, reflex testing of second line agents will be performed and charged.

Method Name

Broth Dilution at Critical Drug Concentrations

Reporting Name

Susceptibility, Mtb Complex, 1 Line

Specimen Type

Varies

Specimen Stability Information

Specimen Type Temperature Time Special Container
Varies Ambient (preferred)
  Refrigerated 

Reject Due To

Agar plate Reject

Clinical Information

Initial treatment regimens for Mycobacterium tuberculosis complex often include isoniazid, rifampin, ethambutol, and pyrazinamide. Susceptibility testing of M tuberculosis complex isolates against these antimycobacterial agents is a key component of patient management.

 

The Clinical Laboratory Standards Institute (CLSI) provides consensus protocols for the methods, antimycobacterial agents, and critical concentrations of each agent to be tested to permit standardized interpretation of M tuberculosis complex susceptibility test results.

 

This test uses an US Food and Drug Administration cleared commercial system for rapid broth susceptibility testing of M tuberculosis complex and assesses resistance to antimycobacterial drugs at the CLSI-recommended critical concentrations.

Reference Values

Results are reported as susceptible or resistant.

Interpretation

Mycobacterium tuberculosis complex isolates are reported as susceptible or resistant to the aforementioned drugs at the critical concentrations.

 

Some experts believe that patients infected with strains exhibiting resistance to low levels of isoniazid but not exhibiting resistance to high levels may benefit from continuing therapy with this agent. A specialist in the treatment of tuberculosis should be consulted concerning the appropriate therapeutic regimen and dosages.

Cautions

Isolates not received in pure culture may have delayed results because isolation is required prior to testing.

Method Description

This test method is based on growth or absence of growth of Mycobacterium tuberculosis complex isolates in broth cultures containing critical concentrations of the antimycobacterial agents isoniazid, rifampin, and ethambutol. One of two FDA-cleared platforms, the BACTEC MGIT 960 (Becton Dickinson) or the VersaTREK (ThermoFisher) will be used. (Brown-Elliott, BA, Cirillo DM, Musser KA, Rowlinson M-C. Susceptibility Test Methods: Mycobacteria, Nocardia, and Other Actinomycetes. In: Carroll KC, Pfaller MA, eds. Manual of Clinical Microbiology, 13th Edition. ASM Press, 2023)

 

The BACTEC MGIT 960 platform measures fluorescence in a Mycobacterial Growth Indicator Tube (MGIT) containing an M tuberculosis complex isolate in the presence of critical concentrations of an antimycobacterial agent. Antimycobacterial agents tested are isoniazid, rifampin, and ethambutol. (Package insert: BACTEC MGIT 960 SIRE Kit, BD Diagnostics, 2016)

 

The VersaTrek platform measures pressure changes inside bottles containing M tuberculosis complex isolates in the presence of critical concentrations of an antimycobacterial agent.  Antimycobacterial agents tested are isoniazid, rifampin, and ethambutol. (Package insert: VersaTREK Mycobacteria Detection and Susceptibility Testing system, TREK Diagnostics, 04/2014)

Day(s) Performed

Monday through Sunday

Report Available

10 to 21 days

Specimen Retention Time

1 year

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test Classification

This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information

87188 x 3-Antimicrobial Susceptibility, Mycobacterium tuberculosis Complex, Broth Method

LOINC Code Information

Test ID Test Order Name Order LOINC Value
TB1LN Susceptibility, Mtb Complex, 1 Line 29579-0

 

Result ID Test Result Name Result LOINC Value
TB1LN Susceptibility, Mtb Complex, 1 Line 29579-0