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The CDC has issued updated its guidelines on testing for TB infections. Published in the June 25, 2010 Volume 59, No. RR-5 issue of Morbidity & Mortality Weekly Report, the report makes recommendations for use of interferon gamma release assays (IGRA) blood tests and tuberculin skin tests (TST) for diagnosing TB infection.
Before 2001, the TST was the only practical and commercially available immunologic test for Mycobacterium tuberculosis infection approved in the U.S., the CDC report says. Recognition that interferon gamma (IFN-?) plays a critical role in regulating cell-mediated immune responses to tuberculosis infections led to development of IGRAs for detection of tuberculosis. IGRAs detect sensitization to M. tuberculosis by measuring IFN-? release in response to antigens representing M. tuberculosis.
In 2001, the QuantiFERON-TB test (QFT) (Cellestis Limited, Carnegie, Victoria, Australia) became the first IGRA approved by the FDA for diagnosing M. tuberculosis infection. In 2005, the QuantiFERON-TB Gold test (QFT-G) (Cellestis Limited) became the second. The CDC published guidelines for using QFT in 2003 and for using QFT-G in 2005.
Antonino Catanzaro, MD, professor of medicine, University of California San Diego, and non-executive independent director of Cellestis Limited, says, "These guidelines encapsulate the enormous body of clinical evidence on the performance of the QFT (QuantiFERON-TB) test and reflect the significant benefits this test is bringing to TB control worldwide."
QuantiFERON®-TB Gold was approved by the FDA in 2007. Tony Radford, chief executive officer, Cellestis Limited, says, "With a specificity of more than 99%, QFT virtually eliminates false positive results and is simple to administer. With more than 400 peer-reviewed, published clinical studies, QFT is a modern, scientifically validated solution for reliable diagnosis of TB infection, and offers significant economic and public health advantages."
The CDA report says updated IGRA guidelines were needed because since 2005, two new IGRAs have been approved by the FDA, and several hundred peer-reviewed articles describing clinical studies of IGRAs have been published. The report provides updated guidance to U.S. public health officials, healthcare providers and laboratory workers for use of FDA-approved IGRAs in the diagnosis of M. tuberculosis infection in adults and children.
The CDC identified relevant reports published through August 2008 by searching PubMed for articles written in English that listed "tuberculosis" as the major MeSH topic and included "QuantiFERON" or "T-Spot" in the title or abstract. The agency identified additional published reports by contacting test manufacturers and examining references listed in retrieved articles. These methods identified 152 potentially relevant articles. The CDC reviewed methods in each study to select 96 primary reports that provided data related to: 1) sensitivity or specificity of QFT-GIT or T-Spot, 2) agreement of QFT-GIT and T-Spot results with each other or with TST results, 3) association of QFT-GIT or T-Spot results with risk for M. tuberculosis infection or subsequent active tuberculosis and 4) evaluation of QFT-GIT or T-Spot use in contact investigations, immunocompromised persons or children.
The CDC used the published reports, data submitted to the FDA, product package inserts and expert opinion related to QFT-GIT and T-Spot to prepare its guidelines. It coordinated development of these guidelines with the American Academy of Pediatrics, the American Thoracic Society and the Infectious Disease Society of America.
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