Transfusion therapy in sickle cell disease

Sickle cell disease (SCD), the most common hemoglobinopathy worldwide after thalassemia, is characterized by a mutation in the beta-globin gene that results in the production of hemoglobin S (HbS). HbS polymerizes under deoxygenated conditions, causing red blood cell (RBC) rigidity that leads to vasoocclusion, hemolysis and endothelial damage. In addition to hydration, pain medication, and diseasemodifying drug therapy, RBC transfusion is a mainstay of treatment. Simple or exchange (manual or automated) transfusions may be performed. RBC transfusions improve blood oxygen content, decrease HbS-containing RBCs, increase HbAA RBCs with normal oxygen affinity, and may suppress endogenous hematopoiesis. The goal of RBC transfusions is to decrease HbS levels to less than 30% and maintain the patient's hematocrit at less than 30%. The choice of performing a simple or exchange transfusion is partly dependent on the indication. Acute indications include acute stroke, acute chest syndrome (ACS), acute multisystem organ failure, intrahepatic cholestasis, hepatic/splenic sequestration, and priapism. Chronic indications include stroke prophylaxis, silent infarcts, recurrent ACS, recurrent painful episodes and complicated pregnancy. The frequency of RBC transfusions and quantity of RBC units transfused should be weighed against the risks of transfusion reactions. Aside from being at risk for the common transfusion reactions such as febrile nonhemolytic transfusion reactions and allergic reactions, patients with SCD are at an increased risk for alloimmunization, autoimmunization, iron overload and delayed hemolytic reactions with hyperhemolysis. This review discusses various aspects of transfusion therapy for SCD.