Evaluation of an interferon gamma assay in the diagnosis of latent tuberculosis infection in patients with rheumatoid arthritis

The tuberculin skin test is not an ideal screening test for the patients with rheumatoid arthritis to identify cases of latent tuberculosis infection (LTBI) prior to the start of treatment with anti-TNFs, as it responds inadequately to late hypersensitivity, which is fundamental for producing a response to the inoculated antigen. Assays based on detection of the production of IFN gamma in vitro by mononuclear peripheral cells stimulated by specific antigens are more specific than PPD in detecting LTBI. The aim of this study was to evaluate the performance of T-SPOT.TB in diagnosis of LTBI in patients with rheumatoid arthritis, comparing with the PPD. The specificity of the T-SPOT.TB varied from 87 to 90% and the negative-predictive value (NPV) from 94.4 to 100%. It can be concluded that the T-SPOT.TB showed high specificity and NPV, proving the capability of identifying false-negative cases of PPD, raising the level of safety for the use of anti-TNFs.