Blood Isn’t Really Blue

Sing along, everyone: A, B, AB, O…

You may have noticed that this is not the typical alphabet song. It’s the blood alphabet, but it’s not as creepy as it sounds. Blood comes in four basic types –A, B, AB, and O– that are based on antigens. An antigen is a substance that causes your immune system to react if it shows up in your body. That’s why, when someone gets a blood transfusion from donated blood, medical personnel have to be careful about who gets what blood.

People with the blood group A have “A antigens” located on their red blood cells. Folks with type B blood have “B antigens” on THEIR red blood cells. What do you think about type AB blood? If you guessed these people have both A and B antigens, you win! Ready for another? What kinds of antigens to people with type O blood have on their red blood cells? Trick question: they don’t have any!

Because antigens involve your immune system, they come into play when you donate or receive blood. Because type O has no antigens, it is considered the “universal donor.” No matter what blood type you have, you can receive it, and your immune system won’t sound the alarm. (Your immune system isn’t going to fight something that’s not present.) Someone with type A blood can donate to anyone with A or AB, and type B can donate to B and AB. People with AB blood can only donate to other AB’s, but they can get blood from anyone since they have both antigens. They are called “universal receivers.”

During transfusions, there’s another antigen to be concerned about: Rh. This comes in two lovely varieties: positive (the antigen is present) and negative (totally missing). You can be O+, or AB-, B-, A+, or any other combination of blood type and Rh factor. Typically, Rh-negative blood is given to people with Rh-negative blood, but people who are Rh-positive can receive Rh+ or Rh- blood.

Getting the right blood type and Rh factor is crucial during a blood transfusion. If the blood is the wrong type and a foreign antigen appears, your immune system kicks in to attack the “invader.” Unfortunately, that can hurt you. Not only won’t your body accept the desperately needed new blood, but, according to theNational Center for Biotechnology Information, an immune system in overdrive can lead to shock, kidney failure, circulatory system breakdown, and even death. Wow. And this is when your immune system is trying to help.