Despite representing a major advance in rheumatology practice, the use of tumor necrosis factor blockade (anti-TNFs) in the treatment of rheumatoid arthritis (RA) has given rise to a problem that was considered solved in many developed countries, i.e. the heightened risk of reactivation of latent tuberculosis infection (LTBI). The identification of cases of LTBI has thus been made obligatory prior to starting any anti-TNF treatment. The cutaneous tuberculin test (PPD) is not the ideal screening test for this group of patients. Low specificity, cross-reactivity with vaccine antigens and other exogenous microorganisms coupled to a defect in the cell-mediated component of the immunological response account for the inadequacy of PPD as a screening tool in this subset of patients. Assays using the detection of in vitro IFNgamma production by peripheral blood mononuclear cells stimulated by specific antigens (ESAT-6 and CFP-10), which are found neither in the BCG vaccine nor in other micro-organisms in the environment should perform better than the PPD, owing to a presumed higher specificity as well as to correlation with indirect measures of exposure to Mycobacterium tuberculosis besides decreased cross-reactivity determined by prior BCG vaccination and/or other infections.
rheumatoid arthritis; tuberculosis; anti-TNF