Question: why we have different blood types like a positive or o negative?

Helen Tunbridge answered on 19 Jun 2013:

There’s not necessarily a why to this, blood cells have different components on their cell surface which are a natural part of cells’ function. These are generally proteins which have different variations. For example the ABO system we hear about for blood types is a protein which has a carbohydrate on it, but there are two variations of carbohydrate that can be attached: the A form and the B form.

The only time you need to worry about which blood type you are is if you are having (or giving!) a blood transfusion. The reason this is important is that you make antibodies (proteins that are involved in protecting you from bacteria and viruses etc) which can be specific for whichever carbohydrate type you *don’t* have. So if you have blood type A and you’re given blood type B, your body has never “seen” that kind of carbohydrate before so it might start an immune response which would make you quite ill. So we check people’s blood types and only give the safe kind of blood.

So the possibilities are A, B, AB (have both the A and B types) or O (don’t have either kind of carbohydrate). So people who have O blood can only RECEIVE O blood, because they have never encountered A or B so it would be dangerous, but because O blood doesn’t have any A or B, it can be given to ANYONE!

The positive or negative you talk about is another kind of protein on the cell called Rhesus factor. Once again, Rh- people can give to anyone (so long as the ABO matches too!) but Rh+ people can only give to Rh+ people.

So the most useful blood is ORh- because it doesn’t have any A/B or Rhesus factor, so that blood can be given to anyone (universal donor). And if your blood is AB+, that’s good news for you because you can be *given* any kind of blood (universal acceptor).

This is a bit of a complicated topic, so I hope I’ve managed to explain it well! Feel free to ask another question if something isn’t clear.