TUESDAY, SEPTEMBER 27, 2016

Data suggest Cepheid Xpert MTB/RIF Assay improves TB tests

The FDA recently approved the Cepheid Xpert MTB/RIF Assay to help physicians determine whether patients with suspected tuberculosis can be removed from airborne infection isolation.

Current Centers for Disease Control and Prevention TB infection-control guidelines recommend isolating a patient suspected of having active TB until clinical and lab data -- including acid-fast bacilli smear testing of three sputum specimens, each collected eight to 24 hours apart -- indicate the patient is unlikely to have contagious TB.

“The revised labeling states that the results from one or two consecutive negative tests using the MTB/RIF will strongly predict the results that would be obtained from AFB smear testing of three sputum specimens for the TB bacteria,” Alberto Gutierrez, director of the FDA Center for Devices and Radiological Health's Office of In Vitro Diagnostics and Radiological Health, said. “This information, along with other patient clinical data, can be valuable in deciding whether a patient can spread TB to other people and whether continued airborne isolation is necessary.”

The Xpert MTB/RIF Assay is manufactured and marketed by Cepheid of Sunnyvale, Calif.

Dr. Philip LoBue, the CDC's director of the Division of Tuberculosis Elimination, is encouraged that a quicker option is now available to detect TB.

“The test may make it possible for some patients to be released from hospital isolation sooner, freeing up limited medical resources and removing restrictions on patients’ movements and interactions,” LoBue said. “While this test can assist health care providers in making important decisions regarding isolation, it does not replace the continued need for culture testing to ensure patients with TB are accurately diagnosed and treated.”

A recent study showed that a single negative MTB/RIF test result predicted the absence of MTB-complex on AFB smears 99.7 percent of the time, while two consecutive negative MTB/RIF test results predicted the absence of the bacteria a staggering 100 percent of the time. Policy dictates that the decision on whether one or two tests are necessary should always be based on the patient and on certain hospital guidelines.

Back in July 2013, the FDA authorized marketing of the MTB/RIF Assay through a regulatory pathway for some low- to moderate-risk medical devices that are not equivalent to devices already approved and marketed. The MTB/RIF test may not detect all patients with active TB, so it is important that health care workers continue to follow current CDC guidelines to collect the sputum specimens for TB culture testing, even if results from the MTB/RIF testing are negative.

It should be noted, however, that the recent findings do not affect current medical practice guidelines for Mycobacterium tuberculosis infection control, but do open the door for future studies.

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