Comparison of the Tuberculin Skin Test (TST) and QuantiFERON ®-TB Gold Test (QFT-G) In Patients With Rheumatoid Arthritis Being Considered for Anti-TNF-Alpha Therapy

In recent years the use of biologic agents for the treatment of rheumatic conditions has called into question the utility of the classic tuberculin skin test (TST) for the diagnosis of latent tuberculosis infection (LTBI). Current clinical rheumatology practice requires potential candidates of biologic therapy to have a negative TST before beginning biologic therapy. But since the TST is time consuming, operator dependent, and fraught with error, it may fail to alert physicians of LTBI in patients with autoimmune diseases and or pharmaceutical immunosuppression. Reactions to intradermal antigen placement requires many cellular interactions, but chiefly they must possess , a sufficient number of memory T cells, the ability to proliferate a clone of T cells specific to the antigen that is introduced, and the ability to traffic these effector cells to the local site. If any of these components are missing the individual may be unable to mount a type IV hypersensitivity (DTH-IV) reaction which is the basis for the TST. While many have recently compared the performance of the new IFN-gamma release assays (IGRAs) like the QuantiFERON-γ TB GOLD® (QFT-G) to the TST for the diagnosis of LTBI, no one has investigated the immunologic factors that may affect these results. Some have postulated that the QFT-G may be less affected by immune-suppression than the TST in patients with rheumatoid arthritis (RA). But recently this was called into question when significant numbers of indeterminate QFT-G results were seen in RA patients. Therefore, we plan to address two current clinical questions. First, what is the best screening strategy for LTBI in RA patients being started on biologic agents - TST, QFT-G or both? Second, is there utility in conducting immune competence testing in RA patients to predict those whom may be unable to generate a positive TST and/or QFT-G. This observational and exploratory pilot study will compare normal matched controls to RA patients being considered for anti-TNF alpha therapy. We will perform a comprehensive evaluation of the immune system by measuring memory T cell numbers with flow cytometry, the ability of memory T cells to proliferate to the tuberculin antigen or purified protein derivative (PPD), and phytohemagglutinin (PHA) antigen via the lymphocyte proliferation assay QunatiFERON-CMI.™ We will also investigate memory T cell trafficking ability via intradermal PPD and PHA antigen placement. Results of QFT-G tests will be compared to the TST with an emphasis on those results which are discordant. We will further attempt to identify immunocompetence testing which may help identify those patients who are unable to mount a DTH-IV response. In order to detect a statistical difference in this specific test population we will use analysis of variance for continuous or ordinal variables and the chi-square test (or Fisher exact test) for categorical data statistics. We hope to contribute to the body of literature regarding the best screening strategy for LTBI in patients with RA, and explore the concept of screening for immune competence in this specific population, which has not been elucidated in the literature.