Haem - transfusion Flashcards
What are the ABO and Rhesus blood group systems?
They are examples of and the most important groups of RBC surface antigens which identify the RBC to the immune system.
How many RBC antigen systems are there and what are these antigens
At least 30
The antigens are polypeptides, polysaccharides or glycoproteins.
Name the minor blood group systems
Kell MNS Lewis P Duffy
What is the H antigen
All patient’s RBC’s have a ‘core antigen’ called the H antigen. The H antigen is a disaccharide.
Describe the ABO system
Group O
- the patient’s only express the H antigen. O signifies no other sugars are added
Group A
- Additional CHO group N - acetylgalactosamine is bound to H antigen making a trisaccharide = The A antigen
Group B
- D-glacatose is bound to the H-antigen –> making a trisaccharide = the B-antigen
Group AB
- These patients express both A and B antigens
What is the Rhesus blood group named after
The Rhesus monkey, the animal whose blood was used in discovery of the Rhesus system
How many different Rhesus antigens are there and which are the most important. Which rhesus antigen is present when patients are referred to as Rhesus positive?
50
Most NB D C c E e
D is most NB. This is the antigen present in patient’s who are referred to as Rhesus positive.
What is the Rhesus D antigen
A large (30 Da) cell membrane protein, thought to be a subunit of the NH3 transport protein. Genetics determine the presence of this Ag on the RBC surface.
85% population are Rhesus D positive
What percentage of population is Rhesus negative
± 15%
Why does the immune system develop antibodies to non-self red cell antigens
- Exposure to foreign RBCs
- Placental abruption
- Blood transfusion - Exposure to environmental antigens (e.g. food / bacteria) –> may be similar to nonself RBC Ag with cross reaction.
Antigen Presenting Cells (APCs) present foreign material to the immune system which then develops antibodies.
At what age are non-self ABO Ag present in the plasma. What antibodies are produced by each blood group
From 6 months onwards (environmental Ag that have a similar chemical structure to ABO Ags)
Group O - Anti A and Anti B
Group A - Anti B
Group B - Anti A
Group AB - none
What type of antibodies are Anti A and Anti B and why is this important.
IgM
This is important as IgM is unable to cross the placenta –> if it could every fetus of different blood group to the mother would have its RBCs attacked by maternal immune system.
How does the development of non-self antibodies differ between the ABO blood group system and the Rhesus blood group system
The 15% of the population who are RhD negative DO NOT naturally develop RhD antibodies. Anti-RhD antibodies are only acquired on exposure to foreign RBCs carrying the RhD Ag.
When can exposure to the RhD antigen occur (i.e. in a Rh negative patient)
- incompatible blood transfusion - RhD pos blood into RhD neg patient
- Fetal-maternal haemorrhage
- After childbirth/abortion/trauma/placental abruption
- If Rh pos fetus and Rh neg mom –> the maternal immune system will then develop anti-RhD antibodies which are IgG and are able to cross the placenta
What type of Antibodies are Anti-RhD and why is this important
IgG
This is important as these antibodies DO cross the placenta. Current and future fetuses can develop haemolysis and severe anaemia and if they survive to term will be born with haemolytic disease of the newborn.
What is RhoGAM?
“rhod Immune globulin human”
This is anti-RhD immunglobulin given to mothers once or twice during pregnancy and at birth in an attempt to prevent maternal sensitization to RhD.
The parenteral anti-RhD IgG binds and removes any fetal RBCs which pass into the maternal circulation.
