Screening for latent tuberculosis infection prior to biologic therapy in patients with chronic immune-mediated inflammatory diseases (IMID): Interferon-gamma release assay (IGRA) versus tuberculin skin test (TST)

Background: The screening for latent tuberculosis infection (LTBI) is mandatory before initiating biologics in patients with chronic immune-mediated inflammatory disease (IMID). The recommendations are based on the tuberculin skin test (TST) and interferon-gamma release assay (IGRA). Aim of the work: To evaluate the agreement between the two tests in the diagnosis of LTBI and to identify risk factors associated with positive TST and IGRA results. Patients and methods: Medical records of 105 IMID patients going to receive a biologic agents were extracted in a cross sectional study (2015-2017). No biologics was undertaken before LTBI screening. All patients underwent IGRA and chest radiography. TST was performed in 94 cases. Results: The mean age of the patients was 47.7 +/- 14.4 years and disease duration of 11.2 +/- 7.6 years. Agreement between the 2 tests results was low (kappa coefficient = 0.08). The sensitivity of TST and IGRA was equally low but the specificity of IGRA was higher. Replacing TST results by positive IGRA showed that number of patients who would take anti-tuberculous chemoprophylaxis will be significantly reduced by 46.5% (from 40.9% to 21.9%; p = 0.0002). TST results were significantly less positive for patients receiving immunosuppressives than for those receiving no treatment (35.1% vs 42.5%, p = 0.031). IGRA results were associated with absence of Bacilli Calemtte-Guerin vaccination. Age was the only risk factor for LTBI associated with both IGRA and TST positivity (p = 0.031, p = 0.011 respectively). Conclusions: TST and IGRA have a low agreement. Both tests should be included in the strategy to diagnose LTBI prior to biologic therapy in IMID patients. (C) 2018 Egyptian Society of Rheumatic Diseases. Publishing services provided by Elsevier B.V.