Low erythropoietin levels are assumed to be the primary cause of anemia, but also decline in iron absorption, bleeding and blood loss during HD sessions, interleukin 6 (IL-6)-mediated hepcidin release by the liver, impairment of erythropoiesis induced by uremic toxins, and deficiency of vitamin B12 and/or folic acid [39]. Here, IL6 is linked to anemia (phenotype).