GSTM1 and chronic kidney disease: The response to oral iron is relatively slow compared to intravenous (IV) iron supplementation [11, 12], with an erythropoietic response to oral iron monotherapy in anemic patients with ND-CKD (defined as an increase in hemoglobin (Hb) of at least 1 g/dL) reported in as few as 14% of cases by 5 weeks [13] and ≤ 30% by 7 weeks [14, 15].