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Major Blood Groups (Substance H (modifiable (enzymatic modification gives…
Major Blood Groups
Substance H
Carb
ubiquitously expressed
visible
modifiable
enzymatic modification gives rise to ABO blood groups
ABO gene
Maps to long arm of chromosome 9
encodes a protein that can posses enzymatic activity (glycosyl transferase)
3 alleles - A, B & O
Allele A
encodes and active enzyme which catalyses transfer of N-acetlygalactosamine to substance H
Allele B
encodes and active enzyme which catalyses transfer of galactose to substance H
Allele O
encodes protein with no enzyme activity
frame shift mutation in gene
substance H remains in native conformation
Red Cell antigens
molecules present on the red cell extracellular surface
visible to other cells and tissues, particularly immune system
Transfusion & Reactions
Anaemia can require a transfusion as it can reduce body's ability to supply O2
Immediate haemolytic transfusion reactions
Usually ABO associated, complement activating
Massive intravascular haemolysis, immediate and life threatening
Naturally occurring antibodies
Phenotype
O
Has O antigens on red cell surface
Has Anti-A & Anti-B antibodies
AB
AB antigens
No naturally occurring antibodies
A
Has A antigens
Anti-B antibodies
B
Has B antigens
Anti-A antibodies
Lab determination of ABO blood group
Indirect antiglobulin test (IAT)
Detection of Anti-A or Anti-B in serum sample
Test serum added to RBC's of known phenotype
Ab's bind
RBC's washed
Anti-human globulin added
Agglutination of RBC's if serum contains Ab's against red cell phenotype