The Blood Type Test is performed to determine a person's blood type representing markers (called antigens) on the surface of red blood cells. This test will tell indicate if you're A, B, AB or O, and whether that blood type is positive or negative.
There are many types of blood, even though they are made of the same elements. There are eight different common blood types. These eight types are determined by the presence or absence of certain antigens. Antigens can trigger responses from the immune system to foreign substances in the body, including transfused blood in a patient.
There are four major blood groups determined by the presence or absence of two antigens (A and B) on the surface of red blood cells. They are:
Group A – has only the A antigen on red cells (and B antibody in the plasma)
- A can donate red blood cells to other As, as well as those in the AB group.
Group B – has only the B antigen on red cells (and A antibody in the plasma)
- B can donate red blood cells to Group B and the AB Group.
Group AB – has both A and B antigens on red cells (but neither A nor B antibody in the plasma)
- AB can only donate to other AB's, but can receive from all other types.
Group O – has neither A nor B antigens on red cells (but both A and B antibody are in the plasma)
- O can donate red blood cells to anybody; it is universal. However, Group O can only receive from others in Group O.
There is also a third antigen called the Rh factor (Rhesus factor) in addition to antigens A and B.
It can be either present (+) or absent ( – ). In general, Rh-negative blood is given to Rh-negative patients, and either Rh-positive blood or Rh-negative blood may be given to Rh-positive patients