Detection of latent tuberculosis infection in rheumatologic diseases before anti-TNFα therapy: tuberculin skin test versus IFN-γ assay.

We aimed to evaluate tuberculin skin test (TST) and interferon-gamma (IFN-γ) test results for latent tuberculosis infection (LTBI) in patients with rheumatologic diseases prior to anti-TNFα therapy. Ninety patients were evaluated in the study at the Departments of Chest Diseases and Rheumatology for anti-TNFα therapy for their rheumatologic diseases. Tuberculin skin test was performed (Mantoux method) and peripheral blood samples were collected for IFN-γ assay (QuantiFeron TB-Gold In Tube) before the anti-TNFα therapy. Of 90 patients, TST positivity was detected in 56 (62.2%) patients, while IFN-γ positivity was detected in 34 (37.8%) patients. Among 56 TST positive patients, IFN-γ positivity was detected in 24 (42.9%) patients, and among 34 TST negative patients, IFN-γ positivity was detected in 10 (29.4%) patients. There was no significant agreement between TST and IFN-γ assay results (Kappa = 0.12, P = 0.2). Forty-three (47.8%) patients were using immunosuppressive drugs owing to their rheumatologic diseases. In this group, TST and IFN-γ positivity is significantly lower than in those who did not receive immunosuppressive treatment (P < 0.05). We conclude that the IFN-γ assay may not be preferred to TST as a diagnostic test in patients with rheumatologic diseases prior to anti-TNFα treatment.