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

Summary 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 in vitro assays are useful methods for LTBI diagnosis in patients with psoriasis, suggesting that they might be less influenced by immunosuppression than TST.