There are four main blood types, which are classified as A, B, AB and O. All blood is also classified according to its Rh factor. The Rh factor refers to the presence or absence of a specific antigen in the blood. Everyone is either Rh positive or Rh negative, meaning they either have the antigen or they do not. A sample of your blood is tested to identify your blood type and Rh factor. Before you receive a blood transfusion, a test is done to establish the compatibility between your blood and the donor's blood.
Whole blood is made up of plasma, red blood cells, white blood cells and platelets.
Donated blood is virtually always separated into components. A person rarely receives a whole-blood transfusion. Usually, a blood component such as plasma or red blood cells is given. You also may receive a combination of components. The type of component you receive depends on your medical condition.