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HelpTest Code MTBXS Mycobacterium tuberculosis Complex, Molecular Detection and Rifampin Resistance, PCR, Sputum
Additional Testing Requirements
Mycobacterial culture is required for epidemiological strain typing and growth-based phenotypic antimicrobial susceptibility testing, including definitive rifampin results as well as results for other antimicrobials. If your facility is unable to perform a mycobacterial culture, order CTB / Mycobacteria and Nocardia Culture, Varies concurrently with this test.
Shipping Instructions
Specimen must arrive within 7 days of collection; if received greater than 7 days from collection, the specimen will be rejected.
Necessary Information
Specimen source is required.
Specimen Required
The high sensitivity of amplification by polymerase chain reaction requires the specimen to be processed in an environment in which contamination of the specimen by Mycobacterium tuberculosis DNA is unlikely.
Specimen Type: Sputum (undigested)
Container/Tube: Sterile container
Specimen Volume: 3 mL
Specimen Stability Information: Refrigerated (preferred) 7 days/Ambient 72 hours
Additional Information:
1. If a single specimen is being shared between mycobacterial culture, acid-fast smear, and/or M tuberculosis PCR, a minimum volume of 3 mL for the respiratory specimen is required. Specimen volumes less than indicated may decrease sensitivity of testing.
2. If insufficient volume is submitted, testing will be canceled.
Specimen Type: N-acetyl-L-cysteine/sodium hydroxide (NALC/NaOH)-digested sputum
Container/Tube: Sterile container
Specimen Volume: 3 mL
Collection Instructions:
1. Submit digested specimen treated with NALC/NaOH.
2. Clearly indicate on container and order form that specimen is a digested specimen.
Specimen Stability Information: Refrigerated 7 days
Additional Information:
1. If a single specimen is being shared between mycobacterial culture, acid-fast smear, and/or M tuberculosis PCR, a minimum volume of 3 mL for the respiratory specimen is required. Specimen volumes less than indicated may decrease sensitivity of testing.
2. If insufficient volume is submitted, testing will be canceled.
Useful For
Rapid detection of Mycobacterium tuberculosis DNA from respiratory specimens for the diagnosis of pulmonary tuberculosis
Presumptive detection of rifampin resistance based on the presence of resistance-associated mutations
Method Name
Real-Time Polymerase Chain Reaction (PCR)
Reporting Name
M tuberculosis/ RIF PCR GeneXpertSpecimen Type
SputumSpecimen Minimum Volume
1.5 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Sputum | Refrigerated (preferred) | 7 days | |
| Ambient | 72 hours |
Reject Due To
All specimens will be evaluated at Mayo Clinic Laboratories for test suitability.Clinical Information
Mycobacterium tuberculosis is a highly transmissible bacterial pathogen and is the causative agent of tuberculosis, a disease causing significant worldwide morbidity and mortality. Each year, M tuberculosis accounts for 1.6 million deaths and is responsible for 10.6 million newly diagnosed cases of tuberculosis worldwide. M tuberculosis is spread from person to person via respiratory transmission and has the potential to become resistant to many of the antibiotics currently used if not treated appropriately. Therefore, rapid and accurate detection of M tuberculosis in patient specimens is of paramount clinical and public health importance.
Conventional culture methods can generally detect M tuberculosis in 2 to 3 weeks, although up to 6 weeks of incubation may be required in some instances. This qualitative molecular assay utilizes polymerase chain reaction-based nucleic acid amplification for the direct detection of M tuberculosis DNA within respiratory specimens without relying on culture growth, leading to more rapid diagnosis and appropriate patient care. This assay also detects the presence of mutations in the rpoB gene that have been documented to confer more than 95% of cases of rifampin resistance.
Reference Values
Negative
Interpretation
A positive result indicates the presence of Mycobacterium tuberculosis complex DNA.
A negative result indicates the absence of detectable M tuberculosis complex DNA.
Presumptive rifampin resistance mediated through mutations within the resistance determining region of the rpoB gene will be reported when detected.
One to 2 negative polymerase chain reaction results in conjunction with 1 to 2 negative acid-fast smears may provide evidence supporting the removal of a patient from airborne isolation. Consult your local Infection Prevention and Control for guidance.
Cautions
This test should always be performed in conjunction with mycobacterial culture, which is required for epidemiological strain typing and growth-based phenotypic antimicrobial susceptibility testing, including definitive rifampin results as well as results for other antimicrobials. If your facility is unable to perform mycobacterial culture, CTB / Mycobacteria and Nocardia Culture, Varies should be ordered.
Per current Centers for Disease Control and Prevention recommendations, rifampin resistance results should be considered as preliminary pending definitive confirmation with gene sequencing or growth-based phenotypic antimicrobial susceptibility testing.
This polymerase chain reaction-based molecular assay detects Mycobacterium tuberculosis nucleic acid and, therefore, does not distinguish between viable, disease-related organisms and nucleic acid persisting from prior infection. Test results should be correlated with patient symptoms and clinical presentation before a definitive diagnosis is made.
A negative result does not rule-out infection with M tuberculosis or active disease because the organism may be present at levels below the limit of detection for this assay.
Method Description
The Cepheid Xpert MTB/RIF assay utilizes sputum or decontaminated and pelleted sputum sediment. Specimens are inoculated directly into single disposable test cartridges, which contain both DNA extraction and target amplification material. The assay amplifies a 192 base-pair segment of the rpoB gene for Mycobacterium tuberculosis complex identification as well as rifampin resistance profiling. The Cepheid Xpert MTB/RIF assay is a closed polymerase chain reaction (PCR) system that greatly reduces the potential for false-positive results due to specimen cross-contamination as compared with traditional open-system PCR methods.(Package insert: Xpert MTB/RIF. Cepheid; GXMTB/RIF-US-10, rev D, 03/2016)
Day(s) Performed
Monday through Sunday
Report Available
Same day/1 daySpecimen Retention Time
7 daysPerforming 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
87556
87798
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| MTBXS | M tuberculosis/ RIF PCR GeneXpert | 89371-9 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| SRCPX | Specimen Source | 31208-2 |
| MTBRX | MTB Complex Result | 88874-3 |
| RIFRX | MTB Rifampin Resistance Result | 89372-7 |
Forms
If not ordering electronically, complete, print, and send a Microbiology Test Request (T244) with the specimen.