TEST CATALOG ORDERING & RESULTS SPECIMEN HANDLING CUSTOMER SERVICE EDUCATION & INSIGHTS
Test Catalog

Test ID: TBPZA    
Susceptibility, Mycobacterium tuberculosis Complex, Pyrazinamide, Varies

Useful For Suggests clinical disorders or settings where the test may be helpful

Susceptibility testing of Mycobacterium tuberculosis complex isolates growing in pure culture against pyrazinamide

 

Confirming Mycobacterium tuberculosis complex resistance to pyrazinamide

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

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

If resistance to Pyrazinamide is detected, the reflex test for confirmation of resistance will be performed and charged separately.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Primary treatment regimens for Mycobacterium tuberculosis complex often include isoniazid, rifampin, ethambutol, and pyrazinamide (PZA). Susceptibility testing of each Mycobacterium tuberculosis complex isolate against these first-line antimycobacterial agents is a key component of patient management.

 

The Clinical and Laboratory Standards Institute (CLSI) provides consensus protocols 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 test results. Current recommendations indicate that laboratories should use a rapid broth method in order to obtain Mycobacterium tuberculosis complex susceptibility data as quickly as possible to help guide patient management. According to the CLSI, resistance can be confirmed by another method or by another laboratory at the discretion of the testing laboratory.

 

This test uses an FDA-cleared commercial system for rapid broth susceptibility testing of Mycobacterium tuberculosis complex against PZA. Since the literature indicates that broth testing of PZA can, at times, produce falsely resistant results, resistance to PZA by the broth method is automatically confirmed by pncA DNA sequencing. The pncA gene of Mycobacterium tuberculosis complex is responsible for activation of the prodrug PZA and hence PZA activity. Mutations in the pncA gene and upstream promoter region have been reported to account for the majority (70%-97%) of PZA-resistant isolates. However, 3% to 30% of PZA-resistant isolates do not have a corresponding pncA mutation and other genes (eg, rpsA) may also play a role.

 

A separate test is available for testing of the other first-line agents (isoniazid, rifampin and ethambutol).

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Results are reported as susceptible or resistant.

Interpretation Provides information to assist in interpretation of the test results

Mycobacterium tuberculosis complex isolates are reported as susceptible or resistant to pyrazinamide at the critical concentration.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

For resistant organisms, confirmatory testing using pncA DNA sequencing is automatically performed and the presence or absence of pncA mutations associated with pyrazinamide resistance is reported.

 

In vitro susceptibility does not guarantee clinical response. Therefore, the decision to treat with a particular agent should not be based solely on the antimicrobial susceptibility testing result.

 

Susceptibility testing should be performed on pure culture isolates of Mycobacterium tuberculosis complex.

 

Some mutations associated with pyrazinamide resistance that may occur outside of the pncA promoter and gene region and may therefore not be confirmed by DNA sequencing of this target.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Blumberg HM, Burman WJ, Chaisson RE, et al: American Thoracic Society/Centers for Disease Control and Prevention/Infectious Diseases Society of America: treatment of tuberculosis. Am J Respir Crit Care Med 2003;167(4):603-662

2. 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

3. Dormandy J, Somoskovi A, Kreiswirth BN, et al: Discrepant results between pyrazinamide susceptibility testing by the reference BACTEC 460TB method and pncA DNA sequencing in patients infected with multidrug-resistant W-Beijing Mycobacterium tuberculosis strains. Chest 2007;131:497-501

4. Chedore P, Bertucci L, Wolfe J: Potential for Erroneous Results Indicating Resistance When Using the BACTEC MGIT 960 System for Testing Susceptibility of Mycobacterium tuberculosis to Pyrazinamide. J Clin Microbiol 2010 Jan;48(1):300-301

5. Campbell PJ, Morlock GP, Sikes RD, et al: Molecular resistance of mutations associated with first- and second-line drug resistance compared with conventional drug susceptibility testing of Mycobacterium tuberculosis. Antimicrob Agents Chemother 2011;55:2032-2041

6. Shi W, Zhang X, Jiang X, et al: Pyrazinamide inhibits trans-translation in Mycobacterium tuberculosis. Science 2011;333:1630-1632

7. CLSI, Susceptibility Testing of Mycobacteria, Nocardiae, and Other Actinomycetes; Approved Standard. CLSI document M24-A2. CLSI, Wayne, PA, 2011

8. LaBombardi VJ: Comparison of the ESP and BACTEC Systems for testing susceptibilities of Mycobacterium tuberculosis complex isolates to pyrazinamide. J Clin Microbiol 2002;40:2238-2239

9. Espasa M, Salvado M, Vicente E, et al: Evaluation of the VersaTREK system compared to the Bactec MGIT 960 system for first-line drug susceptibility testing of Mycobacterium tuberculosis. J Clin Microbiol 2012;50:488-491

10. Somoskovi A, Dormandy J, Parson LM, et al: Sequencing of the pncA gene in members of the Mycobacterium tuberculosis complex has important diagnostic applications: Identification of a species-specific pncA mutation in "Mycobacterium canettiiā€ and the reliable and rapid predictor of pyrazinamide resistance. Confirmation of pyrazinamide resistance is done using Sanger dideoxy sequencing of approximately 700bp of the pncA gene and promoter region. J Clin Microbiol 2007;45:595-599

11. Jureen P, Werngren J, Toro JC, Hoffner S: Pyrazinamide resistance and pncA gene mutations in Mycobacterium tuberculosis. Antimicrob Agents Chemother 2008;52:1852-1854

Special Instructions Library of PDFs including pertinent information and forms related to the test