try to b positive

Do you know your blood type? I do. Turns out, I’m a proud B positive. Representin’ homies.

A few years ago, I had my blood typed out of curiosity. They had to take three vials of blood to complete the test- which I initially found absurd. But when I stopped to think about how the blood typing system works, three vials made sense.

You’ve heard the blood types before: A, B, O, or AB with a positive or negative stuck on the end. What these letters really represent are proteins that belong to the ABO blood group. You see, on the surface of all your red blood cells are imbedded little proteins in the membrane. These are fittingly called- wait for it- surface proteins. They act like identity badges, marking the cell according to which protein floats in the cell membrane. Maybe you have A proteins, or B proteins, or both, or neither. If you have both, you are an “AB” blood type. If you have neither, you are an “O” blood type (O really stands for “none”). So, if you’re “A,” you are technically either “AA” or  “AO.” At the end of the day, you only have “A” proteins so you are just called an “A” bloodtype. Same thing goes for us B types.

There’s another category of surface proteins, known as the Rhesus blood group, or “rh” for short. If you have rhesus proteins, you are “rh-positive.” If you don’t, you are “rh-negative.” This is where the positive/negative part of your blood type comes from.

When blood transfusions take place, phlebotomists must make sure to not give blood with any proteins that the recipient does not originally have. For instance, if you were to give A positive blood to a B negative person, their body would be all “what are these B proteins?! And rh proteins?! Ah HELL no!” and attack those cells. Give that very same person A negative blood, and there’s no problem. Their body would not detect any proteins with which it was not already familiar.

With this knowledge, you can figure out that O negative blood would be accepted by anybody, since it has no proteins for a donor to reject. This is why O negative people are called “universal donors.” Conversely, AB+ blood may only be accepted by AB+ people, since it has all possible surface proteins that could cause a immune reaction. Likewise, AB+ people can accept any blood, since their bodies are already familiar with all three of the possible surface proteins. Ah lah, AB+ people are called “universal recipients.”

All of these proteins are inherited genetically. Each parent can contribute one protein of each category. An “AB” parent can contribute either their A or their B, while an O parent has nothing to offer. So, if Judy (O negative) and Bill (O negative) have a B positive child, Judy got some ‘splainin to do. Blood types were historically used as paternity tests, but as you can see, can sometimes be inconclusive. They are only able to rule out, not determine, a parent- and only part of the time at that.

Armed with the knowledge that there are three possible proteins that may determine a blood type, I understood why that vampire nurse bled me like a stuck pig when I went to get my blood typed. They needed one vial to test for A proteins, one to test for B proteins, and one to test for the rhesus group.

Do you know your blood type? Go find out. Then, I dare you to figure out all the possible blood types your parents could be. It’ll be so much fun!