blood transfusion Flashcards
why is the ABO system important?
people have naturally occurring antibodies against any antigen not present on their own RBCs
describe the properties of the naturally occurring antibodies that work against any antigen not present on someone’s own RBCs.
IgM class
reactive at 37ºC
capable of fully activating complement (so can cause potentially fatal haemolysis if incompatible blood is transfused)
what antibodies are in the plasma of someone with Group A blood cells?
anti-B
what antigens are on the red blood cells of someone with Group A blood?
A
what antibodies are in the plasma of someone with Group B blood cells?
anti-A
what antigens are on the red blood cells of someone with Group B blood?
B
what antibodies are in the plasma of someone with Group AB blood cells?
none
what antigens are on the red blood cells of someone with Group AB blood?
A and B
what antibodies are in the plasma of someone with Group O blood cells?
anti-A and anti-B
what antigens are on the red blood cells of someone with Group AB blood?
none
what is the relative frequency of the blood groups?
O (most common)
A
B
AB
how are A and B antigens on red cells formed?
add one or other sugar residue onto a common glycoprotein and fucose stem (H antigen) on the red cell membrane
group O has neither A nor B sugars; H stem only
how are antigens determined?
through corresponding genes
they code for specific enzymes that add specific sugars to the common H antigen
A and B genes are co dominant
O gene is recessive (i.e someone with group A blood could be AA or AO)
what does the A gene code for?
enzyme that adds N-acetyl galactosamine to the common H antigen
what does the B gene code for?
enzyme that adds galactose to the common H antigen
why is group O blood safe to give anyone in an emergency?
no ABO antigens (antibodies cannot attach anywhere and cause agglutination)
what is the most important antigen?
D
what are the blood groups with reference to the D antigen?
RhD positive (D antigen)
RhD negative (no D antigen)
what genes code for the RhD group?
D codes for antigen
d codes for no antigen, recessive
RhD negative means dd genes
RhD positive means either DD or Dd genes
what is the relative frequency of the RhD positive and negative blood groups in the UK?
RhD positive 85%
RhD negative 15%
what happens if someone with RhD negative blood is exposed to the RhD antigen?
can make anti-D antibodies when sensitised
what type of antibodies are anti-D antibodies and why is this important?
IgG class
can cross the placenta
how can someone with Rhd negative blood end up being exposed to RhD antigens?
transfusion of RhD positive blood
if an RhD negative woman is pregnant with an RhD positive foetus
what are the potential implications of having anti-D antibodies in reference to transfusions?
patient must have RhD negative blood in the future
anti-D would react with RhD positive blood, causing delayed haemolytic transfusion reaction
could cause anaemia, high bilirubin from breakdown of red cells, jaundice etc
