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Transfusion of patients with autoimmune hemolytic anemia is associated with unique risks. Autoantibody often complicates compatibility testing and makes it difficult to exclude the presence of co-existing alloantibodies, thus increasing the risk of a hemolytic transfusion reaction. In addition, the autoantibody itself may shorten the survival of donor red cells. If possible, blood transfusion should be avoided. However, blood should never be denied a patient with a justifiable need even though compatibility testing may be strongly incompatible. When warm autoantibodies complicate compatibility tests, the autoantibody may be absorbed from the patient's serum with their own red cells so that alloantibodies may be detected. When cold auto antibodies are present, compatibility testing is performed strictly at 37 °C. Occasionally, the autoantibody itself has red cell specificity and this is taken into account in selecting the optimal unit of blood for transfusion. Since there is added risk of a hemolytic transfusion reaction, in vivo compatibility testing may be performed in which only a small volume of the selected unit is transfused initially. Prior to proceeding with the remainder of the unit, a blood sample is observed for visual evidence of plasma hemoglobin (and urine, if available. is observed for hemoglobinuria) to exclude the presence of acute intravascular hemolysis. A critical aspect of transfusing patients with AIHA is to avoid over transfusion. The kinetics of red cell destruction always describe an exponential curve of decay, indicating that the number of cells removed in a unit of time is a percentage of the number of cells present at the start of this time interval. Thus, raising the hemoglobin level abruptly is likely to increase the amount of hemolysis that is occurring and may precipitate DIC. Indeed, the most common cause of post transfusion hemoglobinemia and hemoglobinuria in AIHA may not be alloantibody induced hemolysis but rather the quantitative effect of increasing the red cell mass subjected to ongoing autoantibody hemolysis. Accordingly, transfusion of comparatively small volumes of blood is the optimal means of minimizing the danger of transfusion-induced intravascular hemolysis The patient's hemoglobin level should be maintained just above a tolerable level until more specific therapy becomes effective. |
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