Blood Group Systems Usage
Location: Outside U.S.
Date: Summer 2013
What is the difference between MN blood group system and ABO bloodgroup system? Although, we nowadays prefer ABO blood groups why do we use MN blood groups in the forensic department?
Humans actually have multiple blood antigens on the surface of our blood cells. Wikipedia says that there are over 50 different blood group antigens. ABO and Rh are just the most dominant. Rh actually has 3 alleles called C, D and E. So one could be CCddee, for example, but clinically, when referring to Rh, only the D antigen is considered. So MN is another system that is also present. The reason it would be considered in forensics is due to population genetics considerations. Certain combinations are found in different percentages depending on what ancestry a person is a part of. Humans evolved in isolation from each other and until relatively recently, were separated due to difficult travel/migration. But even though we can move around the planet easily now, we still carry the history of our ancestry in our DNA. M and N are codominant, like the ABO system.
When it comes to blood transfusions, blood banks usually only type blood for ABO and Rh. But they never give blood to a patient without doing a crossmatch. This is when they take the blood cells from the donor (which has the antigens) and mix it together with some of the plasma, or liquid part of the blood, which carries the antibodies. If there is a reaction with ANY of the over 50 type of antigens, they would not give that blood to the patient. They would also test to see which antigens may be causing the reaction, so that that patient will know in the future whether they would have reactions in the future. It may be more difficult to find a compatible donor for these people.
Thanks for the question. I am not certain why the MNO blood groupings have changed to the ABO blood grouping. I would recommend looking on the internet for the history of these classifications.
I hope this helps. Please let me know if you have more questions.
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Update: November 2011