IFNG and infection: The EFSA Scientific Opinion on the IFN-γ test (29) states “In infected herds (containing reactors already disclosed by tuberculin tests) the test can be applied in different ways, depending on the suspected level of infection in the herd.” Therefore, to optimize the utilization of the IFN-γ test in infected herds or in OTF herds, an optimal cut-off value or an optimal interpretative criterion could be obtained with the analysis of receiver operating characteristic (ROC) curve (29, 32, 50).