What happens if a person of A+ group blood is given with B+ group blood?

The danger of having a mismatched blood would result to formation of a clot as there will be clumping of blood cells or there will be hemolysis (Red Blood Cell Destruction). It is not a practice nowadays to give blood type O to the other blood groups. A common misconception is that Blood Type O (Universal Donor) and Blood type AB (Universal Recipients). This is a misconception because Type O also has antibodies against A and B blood types and AB has no antibodies but they have surface receptors for Anti-A antibodies and Anti-B antibodies. For example: A donor with blood type O and a recipient with blood type A. Blood type A Red Blood Cells have receptors for the Anti-A antibodies present in Blood type O so there is a danger of these blood cells to clump to each other. The best actually when giving a blood transfusion is that the blood types should always be matched that is Blood Type A should only accept from another Blood Type A, B should only receive from a blood type B. Now, for the + and -; You are said to be positive if your Red Blood Cells have Rh antigens(receptors on the surface of RBC) and negative if you have none. Now for these blood groups it is different when it comes to blood transfusion. A+ can accept blood from an A- blood donor as long as this is the first time he/she receives from an A- blood as the A+ recipient still has no antibodies against A- blood. The second time that A+ needs another blood transfusion it can not already accept blood from an A- donor as the antibodies of A+ will attack the A- RBCs. I hope this is not a little bit too complex alienstar. If you want a more infromation you can post me a message and I'll further explain as I've already taken much space in your discussion lol.

There will be a major transfusion reaction and the red cells would break up and the person will become severely anemic. This can also lead to DIC etc. As the process can be massive it can cause the kidneys to fail, the BP to drop etc. In the modern medical world, its criminal for such a thing to happen!

It can effect badly to that patient if wrong blood is given to him. It will create reaction.

This is due to the reason that, the blood of A Group people contains anti - B antibodies. In B group people there are anti - An antibodies. If we give A group blood to a B group patient, it is bound to be incompatible and will result in serious consequences. Hope this be of help.