I still get blood types mixed up sometimes in my own head. This is why I was glad to hear that the Nobel foundation is hosting a science learning game to help practice blood typing. (If you're viewing this page from a phone or tablet, you might not be able to view the game)
I've embedded the Blood Typing Game below, or you can cruise on over to the link at the bottom of this post to play the game directly from the Nobel Prize website.
This blood typing game sends the lesson home, because it gives you immediate feedback (in the form of a shrieking patient on the operating table) if you mess up the blood type.
Here's how blood typing works, in a nutshell. Your red blood cells have certain antigens on their surface. You also have antibodies in your blood serum. If the antibodies come in contact with antigen of the same type, the result is clumping, which is very inconvenient when it happens inside your blood vessels. This is why blood typing is so important.
If you have A antigens on the surface of your red blood cells, for example, then you cannot give blood to someone who has A antibodies in their blood serum. Likewise, if you have B antibodies in your serum, you mustn't receive blood from someone with B antigens on their red blood cells. This is the basis of blood typing.
If you have A antigens, you will have B antibodies and be considered blood type A
If you have B antigens, you will have A antibodies and be blood type B
Some people have both A and B antigens, and no antibodies. This would make you blood type AB
If you have no antigens and both A and B antibodies, you are blood type O
In addition, there are Rh antigens and antibodies, named for the Rhesus monkey in which they were discovered. The presence or absence of the RH antigens add an Rh+ or Rh- annotation to your blood type, so thre are a total of 8 possibilities.
Someone with blood type O Rh- has no antigens. This makes such a person a "universal donor." You can give blood of this blood type to anyone, because there are no antigens to clump with any kind of antibodies.
Likewise, someone with blood type AB Rh+ can receive blood from anyone, because there are no antibodies in their syrum that would clump with the blood donor's antigens.
Does this sound confusing? I've always found it so, and I have to rethink it every time. The blood typing game helps, so you may want to check it out here: