Blood typing is a method of determining a person's blood type by serological methods. These blood types depend on whether or not there are certain antigens on the red blood cells & if there are antibodies to these substances. Blood Typing is also known as - Cross matching, Rh typing & ABO blood typing etc.

The differences in blood types are due to the presence or absence of certain antigens & corresponding antibodies. Antigens are substances (as a toxin or enzyme) that stimulates an immune response in the body, especially antibody production. The antigens that decide blood types are located on the surface of red blood cells and the antibodies are in blood plasma.

There are more than 20 genetically determined blood group systems known today, but the ABO and Rh systems are the most important ones with serious clinical implications. Not all blood groups are compatible with each other.

According to the ABO blood typing system there are four different kinds of blood types: A, B, AB or O i.e. the null type.

? Blood group A: If you belong to the blood group A, you have type A antigens on the surface of your red blood cells and type B antibodies in your blood plasma.

? Blood group B: If you belong to the blood group B, you have type B antigens on the surface of your red blood cells and type A antibodies in your blood plasma.

? Blood group AB: If you belong to the blood group AB, you have both type A & type B antigens on the surface of your red blood cells and no A or B antibodies at all in your blood plasma.

? Blood group O: If you belong to the blood group O (null), you have neither type A or type B antigens on the surface of your red blood cells but you have both type A & type B antibodies in your blood plasma.

Rh Factor is also an antigen and those who have it are called Rh+. Those who don't have it are called Rh-. A person with Rh- blood does not have Rh antibodies naturally in the blood plasma but a person with Rh- blood can develop Rh antibodies in the blood plasma if he or she receives blood from a person with Rh+ blood, whose Rh antigens can trigger the production of Rh antibodies. A person with Rh+ blood can receive blood from a person with Rh- blood without any problems.

The test sample blood is mixed with three different reagents in 3 different tubes, each containing either of the three different antibodies i.e. A, B or Rh antibodies. The tube in which agglutination occurs indicates that the blood has reacted with the antibodies present in that tube. Based on agglutination patterns, it's very easy to learn your blood type.

One can always give type A blood to people with blood group A, type B blood to a person with blood group B and so on. The transfusion will work if a person who is going to receive blood has a blood group that doesn't have any antibodies against the donor blood's antigens. But if a person who is going to receive blood has antibodies against the donor blood's antigens, the red blood cells in the donated blood will clump.