Question: what happens if you mix two types of blood

Karen answered on 11 Nov 2016:

Hi Killian,
If you mix 2 types of blood (in vivo ie inside the body) that are incompatible this will lead to a transfusion reaction. A transfusion reaction can vary from a slight rise in temperature to death. The reason for the variation in reaction is due to how incompatible the blood is.
There are many blood groups but the most important ones are A B O and Rhesus D. If you transfuse A to an O patient it will have serious consequences, the patients blood will haemolyse and the will very likely die. The same goes for B to O and A to B and vice Versa. O can be transfused to anybody (except Bombay groups who are extremely rare and can only get other Bombay group blood).
The Rhesus part in the negative and positive bit and can cause a severe transfusion reaction if positive is given to negative (but only the 2nd time it is given…the first it just causes the individual to make antibodies).
The less significant blood groups eg M,N,S, Fya etc etc will cause less significant reactions possibly slight fever, feeling unwell for a short time. Hope this helps…it’s complicated but very logical once you get your head around it. All transfusion science is based on immunology principles ie antibody-antigen reactions.