ALS4: Blood Transfusion Flashcards
Why is the ABO system important?
Because people have naturally occurring antibodies against any antigen NOT present on own red cells, from birth.
What immunoglobulin class are the antibodies in the ABO system?
IgM
What is the danger of incompatible blood being transfused?
The antibodies are reactive at 37ºC and capable of fully activating complement, so are able to cause potentially fatal haemolysis (destruction of red cells) if incompatible blood is transfused.
Describe Group A blood type (antibodies in plasma, antigens in RBC)
Antibodies in plasma = Anti-B
Antigens in RBCs = A antigens
Describe Group B blood type (antibodies in plasma, antigens in RBC)
Antibodies in plasma = Anti-A
Antigens in RBCs = B antigens
Describe Group AB blood type (antibodies in plasma, antigens in RBC)
Antibodies in plasma = None
Antigens in RBCs = A + B antigens
Describe Group O blood type (antibodies in plasma, antigens in RBC)
Antibodies in plasma = Anti-A and Anti-B
Antigens in RBCs = None
How are A and B antigens on RBCs formed?
By adding one or another sugar residue onto a common glycoprotein and fucose stem (H antigen) on the red cell membrane.
What is special about Group O?
Group O has neither A or B sugars – H stem only.
How are antigens determined?
By corresponding genes
What does the A gene code for?
An enzyme that adds N-acetyl galactosamine (galnac) to the common H antigen
What does the B gene code for?
Enzyme which adds galactose (gal)
Which genes are codominant?
A and B
Which gene is recessive?
O
Which blood group can be given to anyone in an emergency?
Group O negative blood
What additional classification do blood groups have?
If they are RhD positive or RhD negative
What is the Rh system?
Another antigen called antigen D may or may not be present on RBCs. If it is present it is said to be RhD positive blood and if it isn’t present it is RhD negative.
How is the presence of antigen D determined?
By genes - D gene codes for D antigen on red cell membrane, d gene codes for no antigen and is recessive, Therefore
- Group RhD negative = dd
- Group RhD positive = DD or Dd
What can happen to people who are RhD negative?
They can make anti-D antibodies after they are exposed to the RhD antigen - either by transfusion of RhD +ve blood, or in women if pregnant with an RhD positive foetus.
What class of antibodies are anti-D antibodies?
IgG
What are some implications of anti-D antibodies?
- Future transfusion - patient must have RhD negative blood otherwise anti-D would react with D antigen causing delayed haemolytic transfusion reaction, anaemia etc.
- haemolytic disease of newborn - IgG antibodies can cross placenta.
What do we need to avoid in terms of the Rh system in blood groups?
Avoid sensitisation of RhD negative patients
What must be tested before giving a patient a blood transfusion?
ABO and RhD blood groups on patient’s red cells.
An antibody screen on patient’s plasma (known as ‘group + screen’
Why is an antibody screen performed prior to a blood transfusion?
To exclude any clinically significant immune antibodies.