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P143. Screening for latent tuberculosis in patients with inflammatory bowel diseases: impact of immunosuppressive drugs in the performance of an interferon-gamma release assay

J. Machado, P. Sousa, P. Ministro, A. Silva, Centro Hospitalar Tondela-Viseu, Gastroenterology, Viseu, Portugal


Screening for latent tuberculosis (LTB) is part of routine management in inflammatory bowel disease (IBD) patients before starting therapy with tumour necrosis factor (TNF)-α inhibitors. Whole blood interferon-gamma assays (IGRA) have been developed as an alternative immunodiagnostic approach in LTB screening. QuantiFERON®-TB Gold in-Tube (QTF®) uses an enzyme-linked immunosorbent assay (ELISA) to measure antigen-specific production of interferon (INF)-γ by circulating T cells in whole blood, challenged with Mycobacterium tuberculosis specific antigens (ESAT-6, CFP-10, TB7.7). Peripheral blood is collected into three tubes (test tube, positive control tube - “mitogen” and negative control tube - “nil”). A low response to “mitogen” may occur with insufficient lymphocytes or inability of the patient lymphocytes to generate IFN-γ. This study aimed to determine the impact of immunosuppressive drugs in the performance of QTF®.


The study included patients with a previous diagnosis of IBD who were screened for LTB with QTF®. Clinical data were collected and registered. The amount of IFN-γ released in each tube was measured and registered according to the manufacturer's recommendations and software. In vitro production of IFN-γ in the positive control tube and the final quantitative result of the assay (difference between test tube and “nil” tube) were compared in patients under immunosuppressive drugs and without medication. Different therapeutic regimes were also compared. For statistical analysis SPSS 17.0 was used.


Eighty-three patients were included and 92 QTF® tests were performed. Sixty-one patients (73.5%) had Crohn's disease, 20 (24.1%) had ulcerative colitis and 2 (2.4%) unclassified colitis. The mean age at the time of screening was 35.2±11.9 years. Twenty-nine (31.5%) patients were under immunosuppressive therapy: 17 (18.5%) azathioprine or methotrexate, 10 (10.9%) steroids and 2 (2.2%) with both.

IFN-γ production in “mitogen” tube was significantly lower in patients under imunossupressive therapy with azathioprine or methotrexate when compared with patients without medication. Nevertheless, the final result of the test, when classified as positive, negative or indeterminate was not significantly influenced by immunosuppressive therapy.


In this study the final result of QTF® was not influenced by immunosuppression.