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Clinical Significance of Red Cell Antibodies
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When a physician orders a red blood cell transfusion, the blood bank performs compatibility testing which includes an ABO and Rh type and an antibody screen. The antibody screen detects alloantibodies and autoantibodies in patient plasma. Approximately 95% of patients have a negative antibody screen which means that naturally occurring or expected anti-A and/or anti-B are the only red cell antibodies found in their plasma. If the antibody screen is negative, crossmatch compatible blood can be available within 15 minutes.
But what about those patients whose antibody screen is positive, indicating the presence of an unexpected red cell antibody? The answer is, it depends on the antibody detected. Red cell antibodies are notalike and are categorized according to their clinical significance. Some antibodies are capable of causing hemolytic transfusion reactions and/or hemolytic disease of the newborn and fetus while others are not. The table below categorizes the most common red cell antibodies by their clinical significance.
Significant
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Insignificant
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Duffy (Fya, Fyb)
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A1
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Kell (K,k)
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Bg
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Kidd (Jka, Jkb)
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Chido/Rodgers
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Rh (D, C, c, E, e)
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Csa
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Vel
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HTLA
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JMH
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Kna
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Lewis (Lea/Leb)
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Lutheran(Lua/Lub)
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M,N
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McCa,Yka
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P1
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Sda
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Xga
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If an antibody is clinically significant, the transfusion service needs to provide red blood cells that are antigen negative for the corresponding antibody. For example, if a patient has anti-Kell antibody, they will be transfused with Kell negative blood. When a patient has multiple clinically significant antibodies(i.e. anti-K, anti-E, anti-Fya), the task of finding compatible blood becomes more challenging. Many times a large number of units must be antigen typed to find a single compatible unit of blood. This may necessitate sending the specimen to the consultation lab of our local blood center which maintains a larger inventory of red blood cells. The time required to find a sufficient number of compatible units can range from hours to days depending on the complexity of the case.
If an emergent transfusion is required for a patient with one or more red cell antibodies, the transfusion service may not have time to supply compatible antigen-negative blood. In this situation, the risk to benefit ratio of transfusing incompatible blood to a patient with life threatening hemorrhage must be considered. Transfusion of incompatible blood is usually beneficial in these situations because most clinically significant antibodies do not destroy transfused red cells immediately. The transfusion service at Saint Luke's Hospital and the clinical pathologists are available on a 24x7 basis for consultation.
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