Blood Type Test
Blood type tests are done before a person gets
a blood transfusion and to check a pregnant woman's blood type. Human blood is
typed by certain markers (called
antigens) on the surface of red blood cells. Blood
type may also be done to see if two people are likely to be blood
The most important antigens are blood group antigens
(ABO) and the Rh antigen. So the two most common blood type tests are
the ABO and Rh tests.
The ABO test shows that people have one
of four blood types: A, B, AB, or O. If your red blood cells have:
- The A antigen, you have type A blood. The
liquid portion of your blood (plasma) has
antibodies that fight against type B blood. In the
United States, about 40% of the white population, 27% of African Americans, 28%
of Asians, and 16% of Native Americans are type A.
- The B antigen,
you have type B blood. Your plasma has antibodies that fight against type A
blood. In the U.S., about 11% of the white population, 20% of African
Americans, 27% of Asians, and 4% of Native Americans are type
- Neither the A nor B antigen, you have type O blood. Your plasma
has antibodies that fight against both type A and type B blood. In the U.S., about 45% of the white population, 49% of African Americans, 40% of
Asians, and 79% of Native Americans are type O.
- Both the A and B
antigens, you have type AB blood. Your plasma does not have antibodies against
type A or type B blood. In the U.S., about 4% of the white population,
4% of African Americans, 5% of Asians, and less than 1% of Native Americans are
Blood received in a transfusion must have the same
antigens as yours (compatible blood). If you get a transfusion that has
different antigens (incompatible blood), the antibodies in your plasma will
destroy the donor blood cells. This is called a transfusion reaction, and it
occurs immediately when incompatible blood is transfused. A transfusion
reaction can be mild or cause a serious illness and even death.
Type O-negative blood does not have any antigens. It is called the
"universal donor" type because it is compatible with any blood type. Type
AB-positive blood is called the "universal recipient" type because a person who
has it can receive blood of any type. Although "universal donor" and "universal
recipient" types may be used to classify blood in an emergency, blood type
tests are always done to prevent transfusion reactions.
antigens (other than A, B, and Rh) that occur on red blood cells can sometimes
also cause problems and so are also checked for a match before giving a blood