Question: Why are there different blood types? And why when we get a blood Transplant can we not get different Blood types

Karen answered on 8 Nov 2016:

There are many different blood types and they are determined by the expression of different antigens (proteins) on your red blood cells. The expression of the antigens is based on the genes that you have inherited from your parents. Some blood groups are dominant over other so you will express the dominant gene (e.g. A is dominant over O). Because of this you don’t necessarily have to have the same blood group as your parents, you may inherit a recessive (non expressed) gene from them.
The most recognised blood groups are those which cause transfusion reactions and haemolytic disease of the newborn (HDNB). They are A, B, O and Rhesus D. The Rhesus part is the negative and positive part that people refer to hen saying ” I’m O positive” etc
A transfusion reaction means that if you transfuse an incompatible blood group to a patient (e.g. A to O) they will react badly and v possibly die.
When you are born you have naturally occurring antibodies to group A and B. So if you are group O and the antibodies will attack and kill these blood groups the very first time they are transfused to you . Part of my job is to ensure every patient who needs a blood transfusion gets blood that has been specifically matched to them.
Rhesus antibodies are acquired antibodies (i.e.by receiving an incompatible transfusion or during pregnancy). This means if you are Rh negative the first time you encounter Rh positive cells you will be fine but the next time you encounter them will have a severe transfusion reaction or your Rh positive baby may have HDNB.
If you are group O Rh negative you are called a universal donor and can give your blood to anybody (blood banks LOVE YOU!) . However you can only get your own blood type. If you are one of the rarest blood group AB positive you can get any blood type at all but you can only donate to other AB positive people (blood banks have no time for you!!)
Other blood groups include Kell, Duffy, M,N,S, Lewis, Kidd…etc etc…
Part of my job is ensuring that the correct blood is issued to the correct patient and this is acheived by performing a crossmatch, i.e. mixing the 2 bloods (donor and recipient) together to see if they react in-vitro (outside the body).
I hope this all makes sense, ask again if you need anything clarified.