[The clinical application of quantiferon TB-2G: its usefulness and limitations].

UNLABELLED QuantiFERON TB-2G (QFT) is widely used in clinical settings for the identification of tuberculosis infection because of its high level of utility. It is well known that QFT stimulates peripheral blood lymphocytes in vitro by means of M. tuberculosis-specific protein, and that infection is identified by measuring the interferon-gamma released. Interpretation of QFT results is therefore difficult in immunosuppressed subjects in whom the function of immunocompetent cells, including lymphocytes, is suppressed, making it difficult for them to produce interferon-gamma. There is a high incidence of tuberculosis among hemodialysis patients. It has been conjectured that the use of powerful immunosuppressive agents following kidney transplantation results in a high risk of tuberculosis. How QFT results change immediately following kidney transplantation is an extremely interesting question. In recent years, an increasing number of institutions have been using TNF-alpha inhibitors to treat rheumatoid arthritis patients. Is QTF useful for identifying whether patients have latent tuberculosis infection before the administration of anti-TNF antibodies? In particular, many rheumatoid arthritis patients may have been given methotrexate or glucocorticoids, which suppress the immune system, prior to the administration of TNF-alpha inhibitors, possibly making it difficult to interpret the QFT results. We must be aware of this limitation when performing QFT on immunosuppressed patients. It is also important that we understand the clinical parameters influencing QFT results (such as lymphocyte counts). The morbidity rate of tuberculosis is high among healthcare workers, particularly nurses. A number of studies have reported that QFT is useful in hospital infection control for tuberculosis, but the effectiveness of QFT for monitoring the health of healthcare workers is still not fully understood. In this symposium, we will debate how far QFT can be used and the extent of its usefulness under exceptional circumstances. (1) How do we manage kidney transplant recipients with latent tuberculosis infection? : Norihiko GOTO (Transplant Surgery, Nagoya Daini Red Cross Hospital) It is unclear whether QuantiFERON-second generation (QFT-2G) is useful for diagnostic screening and follow up of latent tuberculosis infection (LTBI) in immunosuppressed kidney transplant (KTx) recipients. The QFT-2G assay that included response to mitogen stimulation was performed before and 6 months after KTx. Non responder was 0 (0%) at baseline, 3 (3%) at 6 months. Response to mitogen stimulation was 9.7 +/- 5.3 IU/mL at baseline vs. 10.4 +/- 5.0 IU/mL at 6 months after KTx (p = 0.29). QFT-2G is a useful screening test for LTBI and active tuberculosis (TB) even during maintenance of immunosuppression of KTx. (2) QuantiFERON-TB Gold in Japanese rheumatoid arthritis patients for assessing latent tuberculosis infection prior treatment of anti-tumor necrosis factor antibody: Shogo BANNO (Division of Rheumatology and Nephrology, Department of Internal Medicine, Aichi Medical School of Medicine) To determine the positive rate of LTBI in RA patients using the QFT-2G test, we divided RA patients into two groups: with or without old TB findings by chest CT. With a cutoff level set at 0.35 IU/ml, the positive rate of QFT-2G in LTBI was detected only 5.8%, when setting cutoff at 0.1 IU/ml (lower cutoff level), 23.1% was detected in LTBI patients. The positive TST results were significantly increased in non-LTBI patients compared than in LTBI patients. The QFT-2G test was not affected by the treatment of MTX, and the incidence of indeterminate result was low. The QFT-2G was useful compared to TST before administration of TNF inhibitors in RA patients, because of superior specificity of QFT-2G. (3) Clinical parameters that influence the sensitivity of T-cell assays: Haruyuki ARIGA (National Hospital Organization Tokyo National Hospital) The detection of tuberculosis (TB) infection in compromised hosts is essential for TB control, but T cell assay might be influenced by the degree of cell-mediated immunosuppression. The relationship between immunocompetence and specific interferon (IFN)-gamma response in whole blood QuantiFERON-TB Gold (QFT) is uncertain. Immune-related clinical indicators associated with the degree of antigen-specific IFN-gamma production were analysed using a large immunologically-unselected population with obvious TB infection. The absolute number of blood lymphocyte in TB patients was significantly associated with specific IFN-gamma production in a linear regression model. Sensitivity of 2 IFN-gamma Release Assays, QFT and ELISPOT, partly depends on peripheral lymphocyte counts. At low lymphocyte count conditions, ELISPOT assay is superior to whole blood QFT for detecting tuberculosis infection. (4) QuantiFERON TB-2G among staffs in the hospitals of Nationao Hospital Organization: Susumu OGURI, Chihiro NISHIO, Kensuke SUMI, Masayoshi MINAGUCHI, Tomomasa TSUBOI, Atuo SATOU, Osamu TOKUNAGA, Takeshi MIYAMOMAE, Takuya KURASAWA (National Hospital Organization Minami-Kyoto National Hospital) PURPOSE To investigate the infection rate of tuberculosis among staffs working in the hospitals of NHO. METHOD Questionnaires were sent to the hospitals and the responses were analyzed. RESULT Among the staffs working in the hospitals with tuberculosis wards, positive rate of QuantiFERON TB-2G was 6.9%, probable positive rate was 5.6%. On the other hand, among the staffs working in the hospitals without tuberculosis wards, positive rate was 4.4%, probable positive rate was 3.9%. CONCLUSION It is necessary to monitor the infection rate among hospital staffs.