What’s the difference between blood types?

By Casey Frye, CCNN Writer

blood cells
The presence of certain proteins – or lack thereof – are what give rise to the different blood types.

If you’ve ever seen a movie with a victim who has lost a ton of blood, one of the first things you’ll hear the fictional doctor say is, “Get me three pints of O-, stat!” As you might have guessed, O- is a blood type… but what exactly are blood types?

First, it’s important to note that everyone’s blood plays the same role, namely: transporting oxygen, delivering nutrients, hauling special chemicals, shipping waste, keeping us warm, and fighting off infections. The real difference comes with the red blood cell – the part of the blood that’s responsible for delivering oxygen – which is coated in proteins called antigens. The antigens serve sort of like an all-access pass to travel inside the blood and throughout the body without getting attacked by the person’s immune system (our body’s defenses against disease).

There are two main types of antigens: A and B. These antigens can exist in different combinations on the surface, which give rise to one important factor in determining blood type. The four main blood types are: A, B, AB, and O. Type A blood means that a person’s red blood cells have the “A” type of antigen on their surface, while having Type B blood means the “B” antigen is on their surface. On the other hand, a person with Type AB blood has both of the antigens on their surface, and Type O blood has neither of the antigens on their surface.

Now, what about all that positive and negative stuff that comes after the blood type? Well, that has to do with a second type of protein marker called the Rh antigen. Basically, if a person has this Rh factor, they have a positive (+) sign tacked on the end of their blood type. If they are lacking in the protein, they get a little negative (-) sign instead. If you do all the combinations right, there are eight blood types in total: A+, A-, B+, B-, AB+, AB-, O+, and O-!

As cool as it is to know a person’s blood type, there is a medical purpose for it. Remember how the antigens serve like an access pass? Well, if a person receives a blood transfusion – blood injected in their bodies from someone else – with the incorrect blood type, the immune system considers it to be a foreign invader and sounds the alarm for attack! Do you know your blood type?

Featured image courtesy of AsaLegault on DeviantArt.