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HelpTest ID TBPZA Susceptibility, Mycobacterium tuberculosis Complex, Pyrazinamide
Infectious
Useful For
Susceptibility testing of Mycobacterium tuberculosis complex isolates growing in pure culture against pyrazinamide
Confirming Mycobacterium tuberculosis complex resistance to pyrazinamide
Additional Tests
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| STVP | Susceptibility, Mtb Complex, PZA | No, (Bill Only) | Yes |
Reflex Tests
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| MTBVP | Mtb PZA Confirmation, pnc A Sequence | No, (Bill Only) | No |
Testing Algorithm
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.
Special Instructions
Method Name
Broth Dilution at Critical Drug Concentrations
Reporting Name
Susceptibility, Mtb Complex, PZASpecimen Type
VariesSpecimen Type: Organism
Container/Tube: Middlebrook 7H10 agar slant
Specimen Volume: Isolate
Collection Instructions:
1. Organism must be in pure culture, actively growing.
2. Place specimen in a large infectious container (Supply T146) and label as an etiologic agent/infectious substance.
Additional Information:
1. Specimen source and suspected organism identification are required.
2. CTB / Mycobacterial Culture or CTBID / Culture Referred for Identification, Mycobacterium must also be ordered and will be charged separately unless identification of organism is provided.
3. See Infectious Specimen Shipping Guidelines in Special Instructions for shipping information.
Forms: If not ordering electronically, complete, print, and send a Microbiology Test Request Form (T244) with the specimen (http://www.mayomedicallaboratories.com/it-mmfiles/microbiology_test_request_form.pdf).
Specimen Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Varies | Ambient (preferred) | |
| Refrigerated | ||
Clinical Information
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 at 300 mcg/mL. 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
Results are reported as susceptible or resistant.
Cautions
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.
Day(s) Performed
Monday through Sunday; Varies
Report Available
10-15 daysPerforming Laboratory
Mayo Medical Laboratories in Rochester
Test Classification
This test has been cleared or approved by the U.S. 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-Susceptibility, Mycobacterium tuberculosis Complex, Pyrazinamide
87153-Mtb PZA Confirmation, pncA Sequencing (if appropriate)