How to Differentiate the Different Blood Types?

Long before the advent of blood typing it was observed that blood transfusions could prove to be fatal in some cases while they can save lives in others. It was the Austrian scientist Landsteiner who first observed that although the basic structure of blood is similar in all humans, there are certain antigens on the surface of red blood cells which may vary from person to person and on mixing two different blood types the blood cells will clump together in the blood vessels causing a fatal reaction. The ABO blood group system is the most important for blood group matching or cross matching before blood transfusion. It is also important in organ transplants, criminal investigations, paternity disputes and anthropological studies. The ABO blood types are type O, A, B and AB.

A person is said to belong to a particular blood group when the red blood cells in his blood express that particular antigen on their surface and have antibodies against the other antigen in the plasma. For example, blood group A individuals express the A antigen on their RBCs and possess anti-B antibodies in their plasma. On the other hand, blood group B individuals express the B antigen on their RBCs and possess anti-A antibodies in their plasma. Blood group AB individuals express both A and B antigens on RBC surface and have no antibodies in their plasma. Blood group O individuals express neither A nor B antigens and have both anti-A and Anti-B antibodies in their plasma. The H antigen is the precursor to the ABO blood group antigens.

The ABO blood types are inherited from genes on chromosome 9 and determined by one out of three alleles (A, B or O) from each parent. A and B alleles are co-dominant and they are both dominant over the O allele. This produces six possibilities of genotypes (AA, AO,BB,BO,AB and OO).Since antigen O is recessive and is not expressed in the presence of A or B antigens, it results in four phenotypes (blood types A, B, AB and O).

The Anti-A and Anti-B antibodies are not present since birth and are influenced by environmental factors unlike the antigens which are completely inherited. They are produced in the first year of life on exposure to food and environmental agents like bacteria, viruses and plants. Anti-A and Anti-B antibodies are IgM type and blood group O individuals can produce IgG type of antibodies. Do to presence of these antibodies in plasma against non-self antigens blood transfusion reactions between different blood groups occur resulting in disseminated intravascular coagulation, shock, acute renal failure and death. Hemolytic disease of newborn occurs in infants of blood group A or B born to mothers with blood group O. It is usually mild and fetal hydrops is rare.

There are four blood types in the ABO blood group system- blood type A, B, AB and O. Blood group O is the universal donor since it expresses no antigen on its RBC surface; hence no antibodies are produced against it. Blood group AB is the universal receiver. If cross matching of blood groups is not done before blood transfusion it can result in serious complications and even death.

Sources:

http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=rbcantigen∂=ch05ABO

http://en.wikipedia.org/wiki/ABO_blood_group_system

http://anthro.palomar.edu/blood/ABO_system.htmhttp://abobloodgroup.googlepages.com/discoveryofabobloodgroupsystem