- Blood Groups

The actual distinctions between the four blood groups,- A, B, AB, and O, has a molecular basis. These different blood types are caused by the presence of a protein cell-surface marker. An antigen (an antigen is something that reacts with an antibodoie) on the surface of the red blood cells' plasma membrane.

When mixed with the wrong blood type, these antigens are picked up by antibodies that cause the cells to clump.

There are four basic types: Type A with A antigens on the red cells and anti B antibodies in the plasma Type B with B antigens on the red cells and anti A antibodies in the plasma Type AB with both A and B antigens on the red cells and no type antibodies in the plasma Type O with no type antigens on the red cells and both anti A and anti B antibodies in the plasma

Someone with type-AB blood can receive any type blood with no ill effects, while people with type-O blood can only take their own type. People with type-A blood can receive A or O, and people with type-B blood can take B or O. Blood donors and recipients must be typed and matched very carefully before transfusions are given.

Group A Blood has A antigen on red cells, and anti-B antibody in its plasma. Group

B Blood has B antigen on red cells, and anti-A antibody in its plasma.

Group AB Blood has both A and B antigens on red cells but neither anti-A antibody nor anti-B anti body in its plasma. AB blood cannot cause the clumping of red cells of any other groups, and therefore persons with AB blood are called universal recipients.

Group O Blood has neither A nor B antigens on red cells, and both anti-A antibody and anti-B antibody in the plasma. Group O blood cannot be clumped by any human blood, and therefore persons with Group O are called universal donors

Before a transfusion is given, it is important to know which blood group a person has because the blood plasma contains strong antibodies, called anti-A and anti-B, that react against the red cells with A or B antigens. If anti-A antibody came in contact with A antigen (or if anti-B antibody met B antigen), the result could be a dangerous, possibly fatal, transfusion reaction. To prevent such reactions, Medical Technologists will "crossmatch" your blood with donated blood. A sample of your blood and samples from donated blood are tested to make certain they are compatible .

Most people also have an another inherited protein of the red blood cells known as the Rh factor, or antigen D. When the D antigen is present, a person's blood type is designated Rh positive. When antigen D is missing, the blood type is classified Rh negative. In general, Rh negative blood is given to Rh negative patients and Rh positive blood to Rh positive patients

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