Scientists are working to grow the rarest blood type in the world in a lab, an effort that could have huge ramifications for medicine. The blood type in question, Rh null, is found in just 50 people ...

A person's blood type is determined by "the presence or absence of certain antigens – substances that can trigger an immune response if they are foreign to the body," according to American Red Cross.

There are different blood types: A, B, AB, and O, with each also being Rh-positive or Rh-negative. Knowing your blood type is important for safe blood transfusions and organ transplants. Type ...