Blood transfusion Flashcards
(37 cards)
How much blood and how frequently can one donor give?
1 unit (1 pint) every 4 months
What glycoprotein and fructose stem is common to everyone?
H stem
What are A and B antigens?
The A and B antigens are made by the addition of a sugar residue onto the common glycoprotein and fructose stem (H stem)
What do the A and B genes encode?
A = An ENZYME that adds N-acetyl galactosamine to the H stem
B = An ENZYME that adds galactose to the H stem
Describe the inheritance pattern of the ABO blood groups.
A and B genes are codominant
O is ‘recessive’ because it doesn’t code for anything at all.
Which antibodies would someone in blood group A possess? Why?
Anti-B antibodies because each person produces antibodies against any antigen that is NOT present on their own red cells.
What class of immunoglobulin are these antibodies? What do they do when they come into contact with their antigen?
IgM They are naturally occurring (nearly from birth) and lead to complete cytokine storm/full activation of complement
They cause haemolysis via complement, This is often FATAL It can lead to cytokine storm, lysis, cardiovascular collapse and death
In the laboratory, what would you see if you were to mix the plasma of someone of blood group A with the red cells of someone in blood group B?
Agglutination - this is done as part of cross-matching donor samples after initial antigen tests.
What are the two most common blood groups in the UK?
A (42%) and O (47%)
What is done before transfusion to check that the donor blood and the recipient’s blood is compatible?
A blood sample is taken from the patient and the ABO blood group is determined (test with anti-A and anti-B antibodies) Select a donor unit of the same group
CROSS-MATCH: patient’s serum is mixed with donor red cells – it should NOT react (if it reacts then it shows that it is incompatible)
Which rhesus antigen is the most important?
RhD
Describe the inheritance pattern of the RhD antigen.
Autosomal Dominant RhD codes for the D antigen
Describe the relative proportions of RhD positive and RhD negative individuals within the population.
RhD positive = 85%
RhD negative = 15%
What can happen when RhD negative people are exposed to RhD positive blood?
They become sensitised and can make anti-D antibodies (IgG)
What are the implications on future transfusions of an RhD negative individual who has been sensitised to RhD following exposure?
In the future they must be transfused with RhD negative blood or the anti-D antibodies, generated from first exposure, will react with the RhD positive blood This will cause a delayed haemolytic transfusion reaction resulting in anaemia, high bilirubin, jaundice etc.
What is haemolytic disease of the newborn?
If an RhD negative mother generates anti-D antibodies following pregnancy with a RhD positive foetus, then if the next foetus is RhD positive, the mother’s anti-D antibodies (IgG) can cross the placenta and cause haemolysis of foetal red blood cells. If severe this can cause hydrops fetalis and death.
About 8% of transfused patients will form antibodies against antigens other than ABO and RhD. What are the implications of this?
Once they have formed antibodies against these other antigens, you must use corresponding antigen negative blood in future transfusions otherwise you risk a delayed haemolytic reaction.
What must you always do before transfusion in patients who are sensitised to rarer antigens?
Before each transfusion you should test the patient’s blood sample for red cell antibodies. So before transfusing a patient, as well as testing the ABO and RhD groups, you must do antibody screening of their plasma.
Why is whole blood no longer routinely given to patients?
It is inefficient
Some components of the blood will degenerate quickly if it is stored as whole blood
What three components is blood first separated into via centrifugation?
Plasma
Platelets (and white cells)
Red Cells
Why are the red cells concentrated and the plasma removed?
It allows you to avoid fluid overloading, which can precipitate heart failure, when giving someone red cells
Red Cells stored at 4c with 5 weeks shelf life
What is fresh frozen plasma (FFP) and what does it contain?
If the plasma is frozen within 6 hours of donation then all the coagulation factors are preserved – this is fresh frozen plasma (FFP)
SHELF LIFE OF 2 YEARS WHEN FROZEN AT -30c, Thawed for 20-30 mins at room temp to preserve coagulation proteins
How is cryoprecipitate produced and what does it contain?
Thawing FFP in a 4 degrees centigrade fridge over night produces Cryoprecipitate
It contains: Fibrinogen Factor 8 Factor 13 Von Willebrand Factor Fibronectin
Explain what fractionation is and why it’s useful.
The plasma of many donors is pooled and put into a fractionating column. This means that various components such as albumin, haemophilia factors and anti-D antibodies can be pulled off.
This is NOT done in the UK.
