GeneXpert MTB/RIF Test
GeneXpert MTB/RIF
GeneXpert MTB/RIF is a new test used for the quick diagnosis of tuberculosis (TB) and drug resistance. This test is rapid and fully automated, detecting drug resistance to rifampicin and acid-fast bacilli in less than 2 hours as opposed to standard cultures, which take 3 to 5 weeks to detect growth and an additional 3 weeks to detect drug resistance.
Getting a GeneXpert MTB/RIF test done is recommended for the diagnosis of tuberculosis disease
Symptoms of tuberculosis
People having primary infections do not usually display any symptoms. During the initial stage, some individuals may exhibit symptoms like low fever, fatigue, and cough. People with active TB show the following symptoms:
Cough
Coughing up mucus or blood
Chest pain
Pain while breathing or coughing
Fever
Chills
Night sweats
Weight loss
Loss of appetite
Tiredness
Test preparation:
No special preparation is required for a GeneXpert MTB/RIF test.
Interpretation of results
The results obtained for GeneXpert MTB/RIF test in case of TB are interpreted as:
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|
MYCOBACTERIUM TUBERCULOSIS (MTB) |
RIFAMPICIN RESISTANCE |
REMARKS |
|
Detected |
Detected |
Target MTB DNA detected is resistant to Rifampicin |
|
Not Detected |
Not Detected |
Target MTB DNA is -not detected |
|
Detected |
Not Detected |
Target MTB DNA detected is sensitive to Rifampicin |
|
Detected |
Indeterminate |
Target MTB DNA concentration detected is very low to determine Rifampicin resistance |
|
Indeterminate |
Indeterminate |
Target MTB DNA could not be detected due to inhibitors |
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|
MTB RESULT |
Ct RANGE (cycle threshold) |
|
High |
<16 |
|
Medium |
16-22 |
|
Low |
22-28 |
|
Very Low |
>28 |
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Deviation from normal levels indicate the following:
·      MTB detected result means that Mycobacterium tuberculosis complex is found.
·      MTB not detected result means that Mycobacterium tuberculosis complex is not found.
·      Detected MTB and Rifampicin resistance (RIF) test result means that the bacteria is highly likely to be RIF resistant.
·      When MTB is detected, but RIF resistance is not detected, the bacteria is most likely RIF susceptible. However, growth-based susceptibility testing to first-line TB medications should be performed on all tests that are positive for MTB.
Results that are MTB-detected and RIF-indeterminate indicate that the test was unable to conclusively determine whether the bacteria was RIF-resistant. First-line TB medications should be tested for growth-based susceptibility.
FAQs
What sample is collected for a GeneXpert MTB/RIF test?
A sputum sample is collected from the patient for a GeneXpert MTB/RIF test
What is the turnaround time (TAT) for the result of a GeneXpert MTB/RIF test?
GeneXpert MTB/RIF test result is usually available within 2 hours of sample collection and processing
What is the advantage of GeneXpert MTB/RIF test?
This test is carried out to ensure quick diagnosis of TB for patients who require immediate treatment because the turnaround time for results from drug sensitivity testing and culture tests can be as long as 4 to 5 weeks. GeneXpert guarantees quick results for patients so they don't have to wait too long, saving both money and time
When is the GeneXpert MTB/RIF test ordered?
For TB and antibiotic resistance detection, the GeneXpert MTB/RIF test is incredibly quick, sensitive, and precise. A doctor may order the GeneXpert test if they suspect that a patient has TB and they want a rapid diagnosis so they can start an effective drug treatment
What are the limitations of GeneXpert MTB/RIF test?
Mycobacterium tuberculosis DNA is detected by GeneXpert MTB/RIF test, which means it cannot differentiate between viable, disease-causing organisms, and nucleic acid left over from earlier infections. Prior to making a final diagnosis, test results need to be compared to the patient's symptoms and clinical presentation.
Additionally, the bacteria may be present at concentrations below the test’s detection limit therefore, a negative result does not exclude Mycobacterium tuberculosis infection or active disease. For epidemiological bacteria strain typing and conclusive drug susceptibility testing, GeneXpert MTB/RIF test is recommended to be performed in conjunction with mycobacterial culture
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