What Would Happen If a Person Received a Transfusion Using a Blood Type Other Than Their Own?

That depends on what type of blood was given and the recipient’s blood type.

There are three major antigens (things on the outside of blood cells that cause allergic reactions). The antigens are A, B, and O. There are two copies. The combos are OO, AO, BO, and AB. They are referred to as O, A, B, and AB for the sake of simplicity.

Type O is tolerated by everyone. Type O blood is “universal donor” and prized. Type A blood is tolerated by A and AB recipients. Type B is tolerated by B and AB recipients. Type AB blood is only tolerated by AB recipients … AB types are “universal recipients.”

So what happens depends on chance:

If a person with AB gets anything different, it does not matter.
If a person with O gets anything different, that’s likely a huge problem called a major hemolytic transfusion reaction.

In a major hemolytic transfusion reaction, the recipient’s immune system vigorously attracts the donated blood. The cells are ripped apart, tons of bad chemicals are released, and the person gets super sick. The kidneys can fail ... first reddish urine then shutdown. The person can develop a severe flu-like illness. They can go into shock and ultimately die. Mortality is high without treatment and considerable even with it.

This is why a mix up is a potentially tragic error.

This post originally appeared on Quora. Click here to view.