GSTM1 and anemia (phenotype): In summary, we recommend that intravenous iron should be used first line in the following IBD patient groups: (1) those with active inflammation; (2) those with moderate to severe anaemia (Hb <100 g/L); (3) those with intolerance to oral iron, including a previous history of intolerance; and (4) those who need erythropoiesis-stimulating agents (ESAs) [23].