The response of patients with inflammatory bowel diseases (IBDs) to anti-tumor necrosis factor alpha (TNFα) agents (infliximab, adalimumab, golimumab, and certolizumab), in terms of the durability of drug therapy, reduction of antibody formation risk, severe infusion reactions, and decrease in hospitalisations, can be improved by the therapeutic drug monitoring (TDM) of blood drug concentrations [1,2]. This evidence concerns the gene TNF and inflammatory bowel disease.