The use of intravenous (i.v.)iron is indicated in patients intolerant to oral iron or when there is a problem of iron absorption (as in celiac disease, inflammatory bowel disease, gastric bypass, chronic inflammatory disease, cancer chemotherapy) or when intestinal blood losses exceed the ability of the normal duodenum to absorb ingested iron (as in obstetrics or surgical blood loss or in Osler-Weber-Rendu syndrome), because it bypasses mechanisms of duodenal absorption and increases Hb levels more quickly than oral iron [51–55]. Here, GSTM1 is linked to inflammatory bowel disease.