The blood types
Your blood type is determined by what kind of antigens your red blood cells have on the surface. Antigens are substances that help your body differentiate between its own cells and foreign, potentially dangerous ones. If your body thinks a cell is foreign, it will set out to destroy it. The ABO blood typing system groups your blood into one of four categories:
- Type A has the A antigen.
- Type B has the B antigen.
- Type AB has both A and B antigens.
- Type O has neither A nor B antigens.
If blood with antigens that you don’t have enters your system, your body will create antibodies against it. However, some people can still safely receive blood that isn’t their blood type. As long as the blood they receive doesn’t have any antigens that mark it as foreign, their bodies won’t attack it.
In other words, donations work as follows:
- O: Type O individuals can donate blood to anyone, because their blood has no antigens. However, they can only receive blood from other type O individuals (because blood with any antigens is seen as foreign).
- A: Type A individuals can donate to other type A individuals and type AB individuals. Type A individuals can receive blood only from other type A individuals and type O individuals.
- B: Type B individuals can donate blood to other B individuals and AB individuals. Type B individuals can receive blood only from type B individuals and type O individuals.
- AB: Type AB individuals can give blood only to other AB individuals, but can receive blood of any type.
Blood types are further organized by Rh factor:
- Rh-positive: People with Rh-positive blood have Rh antigens on the surface of their red blood cells. People with Rh-positive blood can receive Rh-positive or Rh-negative blood.
- Rh-negative: People with Rh-negative blood do not have Rh antigens. People with Rh-negative blood can receive only blood that is also Rh-negative.