Guidelines for using QuantiFERON TB Gold in-tube.

QuantiFERON® TB Gold In-Tube (referred to hereafter as QFT-3G), an improved version of the QuantiFERON® TB-2G (QFT-2G), was approved in April 2009 as a diagnostic kit for extracorporeal tuberculosis (TB) infection. QFT-3G was available for purchase in July 2009. Subsequent problems with blood collection tubes led to the withdrawal of QFT-3G sales; however, it was re-released in January 2010 and is widely available at present. Its predecessor, QFT-2G, had been confi rmed as a TB diagnostic tool not infl uenced by BCG immunization. QFT-3G is increased for diagnostic accuracy by the addition of a new specifi c antigen, TB7.7, along with the other Mycobacterium tuberculosis-specifi c antigens, ESAT-6 and CFP-10. In some areas, QFT-2G tests were diffi cult because transportation of blood specimens to testing laboratories presented an issue related to distance and time. QFT-3G is more user-friendly because the blood collection tubes are precoated with antigens and can be used in most places. Recently, however, it has been determined that the diagnostic accuracy of QFT-3G may be infl uenced by the handling of blood collection tubes, amount of blood collected, mixing and storage of collected blood, and subsequent culture conditions. Accordingly, we need to be aware of quality control for this test from the moment blood is drawn. Another extracorporeal TB infection diagnostic kit, T-SPOT. TB® (T-SPOT, Oxford Immunotec Ltd, UK), is used overseas and will become available in Japan in the near future. The principle underlying the T-SPOT test is identical to QFT-3G: a peripheral blood sample is mixed with ESAT-6 and CFP-10 and the test determines the number of blood cells that produce interferon-γ (IFN-γ), a cytokine that regulates the immune response to M.tuberculosis. Tests of this type are called IFNγ release assays (IGRA)1). TB is diagnosed based on the detection of M.tuberculosis in the patient s blood samples; but in clinical practice, appropriate samples for microbiological diagnosis cannot be obtained many a time, even for patients who are highly suspected for TB. In these cases, IGRAs can be very useful as auxiliary diagnostic tools. IGRA results can be used to diagnose latent tuberculosis infection (LTBI) in persons who were in contact with TB patients by considering the risk of infection based on several factors, including the bacillary excretion status of the index patient, closeness of contact, and history of residence in TB endemic countries. IGRAs can function only as an aid to diagnosis ; active TB disease cannot be diagnosed solely on GUIDELINES FOR USING QuantiFERON® TB Gold In-Tube