Flashcards in Blood Transfusion Deck (48)
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?
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 does the A gene encode?
An ENZYME that adds N-acetyl galactosamine to the H stem
What does the B gene encode?
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
So you need to be homozygous for O (OO) to be in blood group O
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?
They are naturally occurring (nearly from birth)
What would happen if someone with anti-B antibodies was given B-positive blood?
The anti-A/anti-B antibodies are complete antibodies meaning that it fully activates the complement cascade to cause haemolysis of red cells
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?
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?
Describe the inheritance pattern of the RhD antigen.
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
What type of antibody are anti-D antibodies?
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 such patients?
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
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
What three components is blood first separated into via centrifugation?
Platelets (and white cells)
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)
How is cryoprecipitate produced and what does it contain?
Thawing FFP in a 4 degrees centigrade fridge over night produces
Von Willebrand Factor
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.
How many donors does it take to make one unit of red blood cells?
How are red blood cells stored and what is their shelf life?
They are packed cells with the plasma removed and they are stored in a 4-degree fridge
Shelf-life = 5 weeks