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Transfusion science
Blood group
A blood group is an inherited character of the red cell surface detected by a specific
alloantibody
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Most blood groups are organised into blood group systems, each system
represents a single gene or a cluster of two or more closely linked homologous genes
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Most blood group antigens are proteins or
glycoproteins, with the blood group specificity determined primarily by the amino acid
sequence
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These antigens are
not produced directly by the genes controlling their polymorphisms, but by genes encoding
transferase enzymes that catalyze the final biosynthetic stage of an oligosaccharide chain
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The O allele produces neither A nor B
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the product of the A allele is a glycosyltransferase
that catalyzes the transfer of N-acetylgalactosamine (GalNAc) from a nucleotide donor
substrate UDP-GalNAc, to the fucosylated galactose (Gal) residue of the H antigen, the
acceptor substrate
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GalNAc and Gal are the immunodominant
sugars of A and B antigens, respectively
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The ABO gene on chromosome 9 consists of 7 exons
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A and B
alleles are inherited in a co-dominant manner, the O allele by recessive inheritance
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It is synthesised by an alpha
1,2-fucosyltransferase, which catalyses the transfer of fucose from its donor substrate to the
terminal Gal residue of its acceptor substrate
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Two genes produce alpha 1,2-fucosyltransferase; FUT1 responsible
for H on red cells, FUT2 for H in other tissues and in secretions
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Individuals with inactivating mutations in FUT2 lack H, A, and
B from body secretions
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Bombay blood group individuals can only receive
transfusions of Bombay blood group blood
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Newborns develop ABO antibodies through exposure
to the environment
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The antigens of the Rh blood group system are encoded by two genes, RHD and RHCE,
which produce D and CcEe antigens, respectively
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13-p34
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The most significant Rh antigen clinically is D
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The D negative phenotype (Rh negative) is associated with the absence of the
whole D protein from the red cell membrane
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Partial D antigens lack some or most of the D epitopes
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Individuals with partial D
phenotypes must be transfused with D negative blood
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D variants result from amino acid
substitutions in the D protein occurring either as a result of one of more missense mutations
in RHD or from one of more exons of RHD being exchanged for the equivalent exons of
RHCE in a process called gene conversion
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Anti-D can cause severe immediate or delayed
haemolytic transfusion reactions (HTRs) and D positive blood must never be transfused to a
patient with anti-D
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Anti-c may also cause severe HDFN
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Individuals who are Rh
positive can be transfused with Rh positive and Rh negative blood, whereas Rh negative
blood types can only be transfused with Rh negative blood
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Laboratory techniques
Agglutination occurs when antibodies on coated cells form cross-linkages between cells
resulting in visible clumping
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In the laboratory agglutination indicates a
reaction between antibodies in the patient plasma and antigens in the test reagent
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Column agglutination (gel) systems are used to assess agglutination
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Positive
reactions (antibody/antigen interactions) are distinguished by agglutinates near or near the
top of the gel column and negative reactions appear as buttons of red cells at the bottom
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Pre blood donation criteria include; between 17-66 years of age, weigh over 50 kg, Hb >
125g/L for females, and Hb > 135g/L for males
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Whole donor blood is then screened to detect certain viral and bacterial antigens and
antibodies
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Each component has a specific clinical benefit
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Packed red blood cell donations are screened for the presence of hepatitis B surface
antigen, hepatitis C virus antigen, antibody to hepatitis C virus, antibodies to HIV-1 and
HIV-2, syphilis antibody, and human T-cell leukaemia virus antibody
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Packed r

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