The Science of Blood Types

Do you know what your blood type is? A lot of people either know, or THINK they know. Then if you end up being that super popular “O Neg” blood type, you get hounded by the red cross (or local blood donation organization) about donating. But do you know why they want so much O Neg blood? Do you know why we care about Neg vs Pos?

I know exactly what my blood type is. I’m a rare AB Pos. I only know because in school for medical laboratory science we got to draw each other and then type our own blood! It’s a super cool career path if science is your thing! Check out ASCLS – The American Society for Clinic Laboratory Science for some basic info!

Let’s dive in to why O Neg is such a big deal. Essentially it comes down to what ISN’T on the red blood cells of O Neg people and what IS on the red blood cells of other blood types. I will try to keep this in as much layman’s terms as possible. If you don’t understand something, feel free to ask for more clarification! Thinking of proteins, A RBCs (red blood cells) have A proteins on their surface, B RBCs have B proteins, and AB RBCs have both A and B proteins. O RBCs on the other hand don’t have any of those proteins on its surface. Therefore, if you were to mix O blood with any other type of blood, there won’t be any reaction between the two. This get’s a lot more complicated, but we’ll keep it simple for now!

blood type matching nails
My nails match these units of blood!

But why does it have to be Negative? There is another protein involved and it needs to be negative to be universal for all people, the Rhesus Factor. Negative people, if given positive blood, can make antibody proteins that could affect future transfusions. The real danger, however, is when childbearing aged women make the antibody. If they end up with a positive baby, her antibodies can attack and potentially kill the unborn fetus.

This is why antibodies become important as well as your A,B, or O type with transfusion medicine. Naturally, you have the opposite antibody to whatever blood type you are. For example, people with the blood type A have B antibodies in their plasma from birth and people with type B blood of A antibodies. And since we learned that O RBCs don’t have any protein on their surface, they have BOTH A and B antibodies. (AB blood does not have these plasma antibodies and therefore is the universal donor for plasma)

There are also many other different RBC surface proteins that each individual person can have (or not have) and if you get exposed to something you don’t have through a transfusion, you’re likely to make an antibody. And if you receive blood again with that protein you will likely have a transfusion reaction that could be deadly.

This is also why it’s important to have properly trained medical laboratory scientists in transfusion services/blood banks. Nurses are not properly trained for this and neither are doctors.

Now maybe you’re curious about how exactly you get your blood type. It’s all genetics. You get part from your mother and part from your father and together they determine your blood type! This is why if your mother is A and your father is B, you can still come out to be O! Think of it like X and Y chromosomes, except there are 3 different possibilities, ABO. You can be either AA or AO, BB or BO, OO, or AB. People who have O blood can only pass along their O and people who are AB can pass either A or B. Take a look at the punnett square below for an example of the probabilities of what type someone might have.

punnett square for blood types
Punnett square for basic blood type genetics.

Hopefully this helps you understand some of the basic science behind blood types and the process of getting a transfusion. The human body is amazing!

Emily, (ASCP)cm

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