The Detection Of Clinically Significant Antibodies

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The detection of clinically significant antibodies is a crucial step in pre-transfusion testing. There are more than 300 human blood groups, all of which can cause an incompatibility reaction. (Knight 2012) Exposure to incompatible blood groups can also lead to the production of alloantibodies. The two most clinically significant human blood groups are the ABO group and the Rh group. Both of these systems can cause severe and often fatal transfusion reactions, and in the case of the Rh group, due to an incompatibility between mother and the unborn child, it can cause haemolytic disease of the foetus and newborn (HDN). Second only to the ABO group in clinical significance, the Rh group is coded for by two complex, polymorphic genes, RHD and…show more content…
(Lewis et al, 2012) The RHCE protein contains the C, c, E and e antigens. The RHCDE antigen has fewer mutations than the RHD but is no less immunogenic, with the E and c antigens being far more immunogenic than C and e.
Rh group antibodies are usually IgG1 or IgG3 class or a mixture of the two. It is very rare for Rh group antibodies to activate the complement cascade, nor is it known for Rh group antibodies to be naturally acquired. Anti-c and anti-E are the most often Rh group antibodies found post transfusion. Anti-c is also the second leading cause of HDN in the UK. Anti-c is also implicated in more severe haemolytic transfusion reactions. (Knight 2012)
Current antigen/antibody detection tests are based on agglutination reactions. Agglutination is the clumping of antigen-antibody complexes to form insoluble and visible aggregates. Agglutination occurs in two steps. The first step is sensitization, where the antibody present in the serum binds to the antigen sites on the RBC. The second step is “bridge formation”. Antibodies will form cross linking attachments to each other to bind the cells together. The strength and development of the attachments is affected by the class of antibody. IgM class antibodies are large pentameters, they can easily bridge the space between cells and with five arms the can form multiple attachments. Unlike IgG class antibodies, which are monomers and much smaller in size making it more difficult for them to bridge the gaps between cells
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