Iron in sickle cell disease: a review why less is better

Sickle cell anemia (SCA) is an inherited disorder of hemoglobin synthesis that is characterized by life-long severe hemolytic anemia, attacks of pain crisis, and chronic organ system damage. A third of the hemolysis in SCA is intravascular and the resulting urinary losses of iron may lead to iron deficiency. There is no evidence of iron overload in SCA and iron deficiency may be more common than suspected, especially in men. Absence of bone marrow iron remains a gold standard for the diagnosis of iron deficiency in these patients. Although low serum ferritin is highly specific for the diagnosis of iron deficiency, its sensitivity is quite low in SCA because of non-specific elevation due to increased red cell turnover. The kinetics of sickling is strongly concentration dependent such that small decreases in the mean corpuscular deoxyhemoglobin-S concentration (MCHC-S) cause a substantial delay in sickle hemoglobin polymerization. Prolongation of the "delay time of gelation" in excess of the capillary transit time may allow the erythrocyte to traverse the capillary bed to escape to the arterial side before there is rheologic impairment of the erythrocyte from polymerization of sickle hemoglobin. Overt iron deficiency lowers the MCHC-S and thereby decreases the sickling tendency and the severity of hemolysis. The clinical improvement in SCA following the induction of iron deficient erythropoiesis by repeated phlebotomies or by erythrocytapheresis has been reported. Prospective controlled studies are needed to evaluate further, the therapeutic strategy of inducing controlled iron-deficient erythropoiesis in selected patients with SCA.