For emergency transfusions, blood group type O negative blood is the variety of blood that has the lowest risk of causing serious reactions for most people who receive it. Because of this, it's sometimes called the universal blood donor type.
type O, since it contains no antigens. Type O, negative, to be more speciifc (with negative referring to the Rh factor) however O Negative Is widely considered the universal blood type. It is very important because it potentially be transfused to any patient regardless of their blood type. Especially in emergency situations, when there isn't enough time to determine a patients blood type. A person with type O - is considered to be a universal donor because his blood can be safely received by a person with type A, B, AB, or O.
