Out of the total 317 tests, 12 (3.8%) were indeterminate (5 × CD, 4 × RA, 2 × JIA, 1 × AS) (two high spontaneous IFNγ production, 10 low mitogen response). Eleven out of these 12 patients were on combined immunosuppression. Twelve patients (10.5%) (5 × RA, 4 × AS, 2 × CD, 1 × JIA) were positive in the QFT-G in the screening. Four had a negative TST, five a positive, in two the TST was unavailable. From 209 patients investigated during the treatment, 12 were QFT-G-positive. In three of them the initial pretreatment status was known and the QFT-G was negative; however, all three were positive in the TST at 16, 7 and 10 mm. Two of them became QFT-G-positive before the second infliximab infusion, one before the fourth infusion. The remaining nine positive patients had longstanding treatment with different anti-TNF biologicals.
In patients with a positive TST (n = 64), 30 had the QFT-G done before treatment – five had positive results and one an indeterminate result. The remaining 34 TST-positive patients were QFT-G-positive in nine cases and one result was indeterminate. In those who were TST-negative (n = 100), five were positive for the QFT-G. One patient developed TB, TST-negative, QFT-G-positive before therapy.
In patients who were on infliximab and repeatedly investigated, IFNγ production after the nonspecific mitogen stimulation increased: 6.7 ± 3.8 IU/ml, 8.4 ± 2.6 IU/ml, and 8.9 ± 3.4 IU/ml (P = 0.001) before treatment and after 2, and 12 weeks, respectively. No difference was found in IFNγ in longitudinal samples after stimulation with TB antigens.