KYJ 61 - Understanding Blood Groups.
Last month I got a request from a nurse working in an oncology unit with patients needing frequent transfusions. The request was "can you explain some immunology terms and the concept of blood types?"
Bang!! Let's do it.
There are 4 main blood blood groups, and each group has a positive (+) or a negative (-) attached to their group.
The blood group refers to their Red Blood Cells.
In the surface of an RBC there are many chemicals called Antigens. These antigens are like ID badges that allows the body to recognise the RBC as one of its own.
RBCs are like nurses.
Some have ID badges that say "A", some have "B" badges, and some wear both "A" & "B" badges, then there are nurses who never got a badge.
Nurses wearing type A badges are called Type A nurses (type A blood).
Nurses with a type B badge are called Type B nurses (B blood), and nurses with both are called type AB.
Those with no ID badge are called Type O, which means zero. They are not wearing any ID label.
There we have A, B , AB, and O blood groups.
Now here is where it gets tricky.
In people with type A blood, they have an immune fighting chemical in plasma called anti-B antibodies. In People with type B blood, they have anti-A antibodies.
People with type O blood have both antibodies. And AB people have none.
So if I gave you a blood transfusion with an incompatible blood type, then your immune system will attack the "foreign" blood cell's antigen with these antibodies.
B people (because they attack A blood) can't have A blood, or AB blood .
"A" people cant be given B or AB blood,
"O" people fight all other groups so can't have A , B , or AB transfusions.
But AB people can have anybody's blood, because they don't have the AntiA or antiB antibodies. AB people are the easiest to transfuse, and as such, are called the "universal recipient".
In a similar fashion, type O blood people are the "universal donor" because their blood can be given to any one. Often in trauma, when minutes count, a person is given type O blood while the crossmatch blood test is being performed.
Now another antigen on the red blood cell is called a Rhesus factor D. Abbreviated to RhD.
All RBCs may this antigen; in which case they are called RhD(+) or just "positive". If there is no RhD antigen, they are RhD(-) or just "negative".
So we have ABO blood groups and each of these can be RhD positive or negative.
When cross matching blood for transfusions, they match not only the ABO group, but the RhD antigen too.
Any RhD positive blood that is given to RhD negative people can spark a transfusion reaction called a haemolytic reaction, where blood cells explode.
RhD(-) people have an antibody to detect the D antigen and attack it. To suppress this reaction, a negative person can be given an injection of AntiD which inhibits the RhD(-) persons body from making antibodies to fight (+) blood. This really only becomes an issue in negative women giving birth to an RhD(+) baby, where there is a chance during labour that their blood should mix.
So in summary:
B+ blood means that the red blood cell has a B antigen and an RhD antigen on its surface
AB+ blood has all three A, B and RhD.
O- blood in contrast has no antigens. And so if it was given to any one there is no cause to expect a transfusion reaction.
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