Detection of IFN-γ responses for diagnosis of tuberculosis infection in chronic inflammatory disease patients

Objective: Determine IFN-γ responses for latent tuberculosis infection (LTBI) diagnosis in chronic inflammatory disease patients. Material and methods: 89 chronic inflammatory disease patients were classified in 3 groups. Group 1: 53 patients with rheumatic diseases scheduled for anti-TNF-α treatment. Group 2: 23 psoriasis patients, 39.1% were receiving biologic treatments, and 43.5% classic systemic treatments. Group 3: 13 patients with Crohn disease, treated with immunosuppressors. TST was done in all cases. We determined IFN-γ production with Quantiferon-TB Gold In Tube (QFN) and T-SPOT.TB (TS.TB). Results: Group 1: TS.TB, QFN and TST were positive in 20.8%, 17% and 13.2% respectively. We obtained 4 QFN indeterminate results (7.5%) and 2 for TS.TB (3.8%), in all cases TST was negative and corresponded with patients receiving corticoids. Concordance (κ) between TS.TB and QFN was 0.562. Group 2: TS.TB and QFN were positive in 17.14% of the cases. In contrast, TST was positive in 21.74%. Five patients were documented with a previous positive TST. Therefore, when we analyzed patients with IFN-γ assays and TST performed simultaneously, TS.TB and QFN were positive in 5.6% and TST negative in all cases. Concordance between TS.TB and QFN was 100% Group 3: The three assays were negative in all cases. We observed one TS.TB indeterminate result (7.7%) and 2 for QFN (15.4%), corresponding with patients receiving azathioprine. Conclusions: Concordance between both IFN-γ assays was good. Indeterminate results were higher in those patients with Crohn disease. IFN-γ assays, in combination with TST, are useful for the diagnosis of LTBI in patients with inflammatory diseases.