Feb. 26, 2009 The newly introduced Interferon-Y release assays (IGRA) is a new group of blood tests that offer many operational advantages over the conventional tuberculin skin tests (TST) -- particularly in the diagnosis of latent tuberculosis (TB).
An editorial published in Respirology by Wiley-Blackwell discusses the role of IGRA in the diagnosis of TB and brings attention to the potential caveats in the application of these new tests.
"IGRA offers many advantages over TST, such as completion of tests in one visit, availability of results within 24 hours, absence of inter and intra-divergence, ability to detect potential immonu-depression and the avoidance of the booster phenomenon. However, their current cost and the need for delivery of fresh blood limits the feasibility of large-scale application in most TB-endemic areas," said author Professor Chi Chiu Leung of the Tuberculosis and Chest Service, Department of Health, Hong Kong.
TB is an ancient disease that remains a major killer in many parts of the world. It is estimated that one out of ten infected immuno-competent individuals will develop the clinical disease in his or her lifetime.
The ultimate purpose of screening for TB infection is to prevent the onset of the disease. Unfortunately, none of the existing tests for TB infection can distinguish between latent infection and active disease.
"While it is generally difficult to interpret a positive test in TB-endemic areas, IGRA may still play an important adjunctive role for the diagnosis of active TB in children. The new tools offer significant advantages over TST, especially in setting with widespread BCG vaccinations after infancy or revaccinations." said Professor Leung.
He added, "With the various intrinsic limitations present in IGRA, added care should be exercised in the application and interpretation of the new tools. Further studies are required to provide definitive answers and allow these new tools to be applied more effectively."
This paper is published in the January 2009 issue of Respirology (Vol. 14, Issue 2).
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