What Are Blood Types?
Every person has a blood type. There are four major types, each with a different chemical marker that's attached to the red blood cells. These markers determine if someone has type A blood, type B blood, type O blood, or type AB blood. Each blood type can also be positive (+) or negative (-), just to make things a little more complicated!
It's important that doctors know which blood type you have if you're going to have surgery, just in case you need some extra blood. But in an emergency, anyone can safely receive O negative blood, regardless of their blood type.