Bench-to-bedside review: iron metabolism in critically ill patients.
Iron kinetics and metabolism are most critical issues in the care of intensive care unit patients but also postoperatively and in any situation where acute inflammatory reactions occur. The problem is that in many patients severe anemia develops due to inhibition of endogenous erythropoietin (EPO) production and iron availability but nobody really knows whether and how this anemia should be treated. Besides blood transfusion, which probably does more harm than good, oral and intravenous (IV) iron are other options.
Generally, as the authors say, iron administration might be a problem in case of underlying bacterial infection since bacteria such as staphylococci use iron for proliferation, e.g. it was shown that staphylococci use iron directly from erythrocytes out of the heme protein. One would not like to feed these bacteria with additional iron.
If bacterial infection is ruled out, especially IV iron in combination with recombinant human erythropoietin (rHuEPO) is an option, because oral iron will probably not be absorbed due to increased hepcidin levels which inhibit iron absorption.
IV iron will be delivered directly for erythropoiesis and rHuEPO will substitute missing endogenous EPO. Our group could show this effect in postoperative anemia in postpartum patients.
Finally, it is not easy to assess iron stores and kinetics because high serum ferritin levels frequently result from inflammation. Here additional tests will be needed such as hypochromic red cells to assess functional iron deficiency and ideally soluble transferrin receptors, since they are not influenced by inflammation. However, the link between hypochromic red cells and inflammation has been discussed for years and is still under investigation. We first reported on the subject in 1999 (Lancet, Vol. 353, 841-842) in response to Bellamy et al. (Lancet 1998, Vol. 352, 1903).
– Christian Breymann