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Test ID: TB2LN Susceptibility, Mycobacterium tuberculosis Complex, Second Line, Varies


Useful For

Determination of Mycobacterium tuberculosis complex minimal inhibitory concentrations to second-line antimicrobial agents

Additional Tests

Test ID Reporting Name Available Separately Always Performed
STV2 Susceptibility, Mtb Cx, 2nd Line No, (Bill Only) Yes

Testing Algorithm

When this test is ordered, the additional test will always be performed at an additional charge.

Reporting Name

Susceptibility, Mtb Complex, 2 Line

Specimen Type


Additional Testing Requirements

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 unless identification of organism is provided. 

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. 

Specimen Stability Information

Specimen Type Temperature Time Special Container
Varies Ambient (preferred)

Clinical Information

The Clinical and Laboratory Standards Institute (CLSI) provides a consensus protocol for the methods, antimycobacterial agents, and critical concentrations of each agent to be tested in order to permit standardized interpretation of Mycobacterium tuberculosis complex susceptibility testing results. CLSI guidelines suggest that second-line agents should be tested when an isolate of M tuberculosis complex is resistant to rifampin, is monoresistant to the critical concentration of isoniazid and the physician intends to use a fluoroquinolone for therapy, or is resistant to any combination of 2 first-line agents.


This test uses a broth microdilution method for susceptibility testing of M tuberculosis complex against second-line agents. Agents tested are amikacin, ethionamide, kanamycin, moxifloxacin, ofloxacin, p-aminosalicylic acid, rifabutin, and streptomycin. In contrast to other M tuberculosis complex susceptibility methods which test 1 or 2 critical concentrations of a drug, this method examines a range of drug concentrations and produces a minimal inhibitory concentration result.

Reference Values

Results are reported as minimal inhibitory concentration (MIC) values with units of mcg/mL and tentative interpretations of susceptible or resistant are provided.


Results are reported as minimal inhibitory concentrations (MIC) in mcg/mL and tentative interpretations of susceptible or resistant are provided.



MIC range tested


MIC tentative interpretations (mcg/mL)*














>5 .0













Para-aminosalicylic acid


















< or=42




< or=1


*Laboratory-derived tentative interpretations based on MIC breakpoints established relative to the indirect agar proportion method; consensus breakpoint interpretations are not available at this time.(1)

**This test is used as an alternative to TB1LN / Antimicrobial Susceptibility, Mycobacterium tuberculosis Complex, First Line, Varies when reagents are not available to perform the TB1LN test. These agents are not routinely reported with this test.

Clinical Reference

1. Hall L, Jude KP, Clark SL, et al: Evaluation of the Sensititre MycoTB plate for susceptibility testing of the Mycobacterium tuberculosis complex against first- and second-line agents. J Clin Microbiol 2012;50:3732-3734

2. Centers for Disease Control and Prevention. Treatment of Tuberculosis, American Thoracic Society, CDC, and Infectious Diseases Society of America. MMWR 2003;52(No. RR-11):1-79

3. Woods GL, Lin S-Y G, Desmond EP: Susceptibility test methods: Mycobacteria, Nocardia and other Actinomycetes. In Manual of Clinical Microbiology. 10th edition. Edited by J Versalovic, KC Carroll, G Funke, et al: Washington, DC, ASM Press, 2011, pp 1215-1238

4. CLSI. Performance Standards for Susceptibility Testing of Mycobacteria, Nocardia species, and Other Aerobic Actinomycetes.First editionCLSI supplement M62. Clinical and Laboratory Standards Institute; 2018

Day(s) Performed

Monday through Sunday

Report Available

21 to 30 days

Test Classification

This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information

87186-Susceptibility, Mtb Cx, 2nd Line

LOINC Code Information

Test ID Test Order Name Order LOINC Value
TB2LN Susceptibility, Mtb Complex, 2 Line 29579-0


Result ID Test Result Name Result LOINC Value
TB2LN Susceptibility, Mtb Complex, 2 Line 29579-0

Method Name

Minimum Inhibitory Concentration (MIC) by Microtiter Broth Dilution Method

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