Diagnosis of tuberculosis infection by interferon-gamma release assays in patients with psoriasis

Objective: In this study, we have performed a direct comparison between both T-cell based assays (QFN-G-IT and T-SPOT.TB) and TST in patients with psoriasis taking different immunosuppressant drug-regimens. Methods: We have prospectively studied 103 patients with moderate-to-severe psoriasis who required latent tuberculosis infection (LTBI) screening before starting systemic immunosuppressive treatment or during its sustained use. Results: Overall number of positive results was 16.5%, 17.5% and 8.7% using T-SPOT.TB, QFN-G-IT and TST, respectively. Differences in the percentage of positive results between TST with T-SPOT.TB and QFN-G-IT were significant (. p=0.005 and p=0.008, respectively). A total of 24.3% of the subjects enrolled were positive for at least one of the three tests performed. Sixteen patients with negative TST (17%) were positive for one of the two IGRAs. We obtained seven indeterminate results by T-SPOT.TB and two by QFN-G-IT. Seven patients with negative TST presented indeterminate results by either of two IFN-γ assays. Positive TST, T-SPOT.TB and QFN-G-IT results were not affected by clinical therapeutic profile. Conclusions: Our results reveal that invitro assays are useful methods for LTBI diagnosis in patients with psoriasis, suggesting that they might be less influenced by immunosuppression than TST.