BACKGROUND: During screening for latent tuberculosis infection (LTBI), before anti-tumor-necrosis-factor-a treatment, most patients are already receiving immunosuppressive therapy. The objective was to evaluate the performance of the QuantiFERON Gold In-Tube (QFT-IT) and the Tuberculin Skin Test (TST). METHODS: A prospective multicenter study included 248 patients with ulcerative colitis (39), Crohn's disease (54), rheumatoid arthritis (111), and spondylo-arthropathy (44). RESULTS: QFT-IT was positive in 7/248 (3%), negative in 229 (92%), and indeterminate in 12 (5%). TST was positive in 54/238 (23%) patients. Chest x-ray was suspect for tuberculosis in 5/236 (2%), and 35/167 (21%) had =1 risk-factors for infection with Mycobacterium tuberculosis. The main finding was a pronounced negative effect on QFT-IT and TST performance associated with prednisolone treatment. During prednisolone treatment interferon gamma (IFN-¿) response to mitogen stimulation was impaired (median IFN-¿ response 4.9 IU/mL; interquartile range [IQR] 0.8 to =10.0) compared to patients 1) not receiving corticosteroids (median =10.0; IQR 5.0 to =10.0; P = 0.0015) or 2) receiving long-acting corticosteroids (median >10.0; IQR 9.7 to >10.0; P = 0.0058). Prednisolone treatment was strongly associated with negative TST, adjusted odds ratio (AOR) 0.22 (0.1-0.8; P = 0.018), and with an increased risk of indeterminate QFT-IT results AOR 16.1 (4.1-63.2; P < 0.001), whereas no negative effect was found for long-acting corticosteroids. Doses of =10 mg prednisolone were associated with a 27% risk of indeterminate results. Single use of azathioprine, methotrexate, or 5-aminosalicylate (5-ASA) did not affect the test results. CONCLUSIONS: Oral prednisolone severely suppressed QFT-IT and TST performance, whereas the long-acting corticosteroids methotrexate, azathioprine, and 5-ASA did not have a similar detrimental effect. Patients should be screened for LTBI with QFT-IT or TST prior to initiation of prednisolone therapy and negative QFT-IT or TST results interpreted with caution in patients treated with any corticosteroid until further data are available. (Inflamm Bowel Dis 2011).