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Sickle cells are prematurely removed from the circulation by the spleen, resulting in hemolytic anemia. The circulating half life of sickle cells is 16 to 20 days, which is much less than the normal half life of 120 days for normal RBCs. RBCs can be transfused as a simple transfusion or via exchange transfusion. A simple transfusion involves transfusing one or two units of RBCs through a peripheral IV. Exchange transfusion is usually performed using an automated apheresis machine that replaces one to two patient RBC volumes with donor RBCs. Indications for transfusion in sickle cell disease include:
During transfusion of patients with splenic sequestration, the hemoglobin often increases beyond the expected level, so it is important to transfuse slowly to avoid over-transfusion. Simple transfusion or exchange transfusion should be considered for patients with refractory priapism. Exchange transfusion has been associated with adverse neurologic sequelae, such as seizures and increased intracranial pressure, so this alternative should be reserved for the most refractory cases. Patients with sickle cell disease are at high risk for complications during major surgery. Some practitioners recommend that patients be transfused to a hemoglobin of 10 g/dL prior to surgery. Exchange transfusion is not necessary. Patients with the acute chest syndrome benefit from transfusion early in the course of their disease. Simple transfusion is preferred for patients who are stable. Simple transfusion should only be performed until the hemoglobin reaches about 10 g/dL. Higher levels are associated with vaso-occulsion. Exchange transfusion is recommended for patients who have a rapidly evolving course or do not respond to simple transfusion. There does not appear to be any role for transfusion in the management of routine, uncomplicated painful crises. Adverse Consequences of Sickle Cell Disease Transfusion Adverse consequences of Sickle Cell Disease Transfusion include alloimmunization, hyperhemolysis and iron overload. Patients with sickle cell disease are chronically transfused and have a high rate of alloimmunization (18-36%). Most patients with sickle cell disease in the United States are African American, and most donors are Caucasian from Western European descent. As a result of this ethnic difference, patients with sickle cell disease are exposed to RBC antigens that they lack, increasing the likelihood of alloantibody formation. The most common antibodies formed in this population are C, E,K1 and Fya . In order to prevent alloimmunization, some centers routinely perform RBC phenotypes on patients with sickle cell disease and only transfuse RBCs that lack C, E,K1 and Fya , if the patient is negative for these antigens. This strategy reduces the rate of antibody formation. A complimentary strategy is to recruit donors who are ethnically similar to sickle cell patients, thereby increasing the likelihood that donors and patients are more antigenically similar. A serious type of hemolytic transfusion reaction, called the hyperhemolytic syndrome can occur during Sickle Cell Disease Transfusion. In this syndrome, a patient’s hemoglobin falls, instead of rises, after transfusion. Both the patient’s own RBCs and the transfused RBCs are destroyed even though the transfused RBCs are crossmatch compatible and no new alloantibodies are detectable at the time of transfusion. Further transfusion compounds the problem. Therefore, it is important to recognize this syndrome early and, if possible, discontinue transfusion. If additional transfusions are required because of life-threatening anemia, they should be done cautiously, using concurrent IVIG and steroids. Each unit of transfused RBCs contains about 200 to 250 mg of iron. With chronic transfusion, iron accumulates in the heart, liver, and endocrine glands. In order to prevent this complication, iron chelating medication is administered. Serum ferritin is serially measured to assess iron stores. Transfusion Recommendations Patients with sickle cell disease should not be transfused with RBCs containing Hgb S. Therefore, many laboratories test donor units with a simple solubility test and select units that lack Hgb S. Patients with sickle cell disease should also be transfused with leukocyte reduced blood products to decrease the risk of cytomegalovirus (CMV) transmission, febrile non-hemolytic transfusion reactions, immune suppression, HLA alloimmunization and RBC alloimmunization. RBCs selected for Sickle Cell Disease Transfusion should be:
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