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Xpert MTB/RIF is a new automated test for detecting TB bacilli and to evaluate if resistance to rifampicin is present.

What is the major advantage of Xpert MTB/RIF?

Xpert MTB/RIF is the most rapid test for the detection of tuberculosis and the results are available in less than 2 hours. Besides having high sensitivity and specificity, the test can be done at the point of care without access to sophisticated laboratories. Drug resistance to rifampicin, one of the principal anti-TB drugs can also be detected within 2 hours while conventional methods to detect drug resistance which may take weeks to months.

What is the sensitivity of Xpert MTB/RIF?

The sensitivity in smear positive tuberculosis is 98.2% in a single direct test. In smear negative tuberculosis the sensitivity is 72.5% for a single test but improves to 90.2% if three tests are performed. The accuracy of detecting rifampicin resistance is 97.6%.

How is Xpert MTB/RIF helpful in HIV patients with suspected tuberculosis?

Tuberculosis is common in HIV positive individuals but diagnosis of tuberculosis in HIV patients is difficult due to the disproportionate smear negative cases and anergy to tests like mantoux. The sensitivity of Xpert MTB/RIF among HIV positive patients with tuberculosis is 93.9%.

How does Xpert MTB/RIF work in detecting resistance?

In Xpert MTB/RIF the mycobacterium tuberculosis specific rpoB gene is extracted and amplified using real time polymerase chain reaction (PCR). DNA probes which emit light are used to probe for mutations within the rifampicin resistance determining region.