The Food and Drug Administration is allowing the maker of a tuberculosis test to expand its product's claims, hoping to help physicians more rapidly determine whether TB patients are contagious.
Sunnyvale, Calif.-based molecular diagnostics firm Cepheid can now expand claims that allow doctors to use one or two negative results of its Xpert MTB/RIF test to determine if a patient showing signs of tuberculosis should continue to be kept in a hospital airborne isolation room.
“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 (acid-fast bacillus) smear testing of three sputum specimens for the TB bacteria,” said Alberto Gutierrez, director of the Office of In Vitro Diagnostics and Radiological Health at the FDA's Center for Devices and Radiological Health.
“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,” he said in a statement.
Cephied originally received FDA approval to market MTB/RF in 2013. It was labeled as the first FDA-reviewed test that could both detect for tuberculosis bacteria and determine whether the bacteria would be resistant to rifampin, an antibiotic used to treat TB.
Current TB infection-control recommendations issued by the Centers for Disease Control and Prevention (PDF) call for placing a patient suspected of having TB in airborne isolation until three specimens from an acid-fast bacillus smear test yield a negative result.
Specimens must be collected between eight and 24 hours apart, requiring a patient to remain in isolation for a minimum of several days until a determination on his or her condition can be made.
The MTB/RIF differs from the smear test in that it tests for the DNA of the mycobacteria that cause TB, allowing for tuberculosis detection even when an AFB test may come back negative. Test results can be delivered in less than two hours, according to the Cepheid website.
“This claim expansion significantly extends the diagnostic utility of Xpert MTB/RIF for U.S. hospitals,” said Cepheid's CEO John Bishop in a statement released Friday. “Placing patients in respiratory isolation is expensive for healthcare facilities and can impede patient care.”
The FDA decision to allow Cepheid to expand use claims for its test was based on results from a large clinical study in which patients were tested to see if they were TB-negative with MTB/RIF, along with a traditional smear test. One MTB/RIF negative result was 99% effective in determining if a patient did not have TB, while two consecutive negative MTB/RIF test results were able to predict the absence of TB bacteria at a rate of 100%.
But testing with the MTB/RIF alone was not recommended by the CDC, since it cannot detect active TB in the lungs of up to 15% of patients.
“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,” said Dr. Philip LoBue, director of the CDC's Division of Tuberculosis Elimination in a statement. “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.”
The new expanded-use claims are expected to be added to the product as soon as Feb, 17, according to the company.
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