Blood Transfusion Flashcards
Why is the ABO blood group system important?
From birth people have naturally occurring antibodies against any antigen not present on your own RBCs
The antibodies are IgM class, reactive at 37 degrees C and can fully activate complement. So they are able to cause potentially fatal haemolysis if incompatible blood is transfused
What are the blood groups and what antigens do they have?
Group A
Has A antigen on it, and Anti-B antibodies in the plasma
Group B
B antigen on it. Anti A in the plasma
Group AB
A and B antigen on it. No antibodies in plasma
Group O
No antigens, A and B antibodies in plasma
What are the percentages of the population woth each blood type?
O - 46%
A - 43%
B - 8%
AB - 3%
How are the A and B antigens on RBCs formed?
Adding A or B sugar residues onto a common glycoprotein and fucose stem (H antigen) on the cell membrane
Group O has neither sugars, only the H stem
How are blood antigens determined?
Genes
- The A gene codes for an enzyme that adds N-acetyl galactosamine to the common H antigen
- The B gene codes for an enzyme that adds galactose
A and B genes are co dominant.
O gene is recessive
How do blood tests work?
Eg a group B person has anti A antibodies
If you add their blood to group A cells, agglutination will occur visibly so yk it’s incompatible
What is the most important blood antigen? What are the associated blood groups?
D
RhD positive (with D antigen)
RhD negative (w/o)
What are the genes for the RhD group?
D gene codes for D antigen (dominant)
d gene codes for no antigen (recessive)
What are the Abundances of the RhD groups in the population
RhD + (85%)
RhD - (15%)
(Negative can make anti D antibodies if sensitised)
What might RhD people produces anti D antibodies?
Transfusion of blood from someone who is RhD positive
In women who are pregnant with an RhD positive baby
They are IgG class antibodies
What are the implications of sensitisation of anti D antibodies?
- Future transfusions: in first they need RhD negative blood. Otherwise anti D would react with RhD positive blood. Causes delayed haemolytic transfusion reaction (anemia, high bilirubin, jaundice)
- HDN - haemolytic disease occurs the newborn: if the RhD negative mum has anti D. In The next pregnancy the IgG antibody will enter the placenta (only this class can do this), art ach to the baby’s RhD + RBCs and cause haemolysis. If severe, Hydrops fetalis, and death. If not brain damage when born
Which are the universal donors and acceptors?
AB - acceptor
O - donor
Are there other blood antigens?
Yes
But we don’t match them
about 8% of blood recipients form antibodies to one of these
What tests are carried out before a blood transfusion?
ABO and RHD groups
Antibody screen
What is the antibody screen for?
Exclude any clinically significant immune antibodies
Patient plasma is incubated with two or three different fully typed screening red cells which are known to possess all the blood-group antigens which matter clinically
If it is negative any donor blood which is compatible can be given. If the screen is positive the Antibody must be identified with use of the large panel of red cells donor units of blood lacking the corresponding blood-group are chosen
