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Your red blood cells contain special molecules on the surface. These molecules are part of your “self”. Therefore, it is not attacked by your immune system. However, if you get a transfusion with blood containing surface molecules that your body does not recognize, it will treat it as an antigen and destroy the blood cells. This reaction is serious and can cause death. 

There are 8 blood types, namely positive and negative versions of A, B, AB, and O type. The blood type is positive if it has a certain protein attached to the surface called Rhesus (Rh) factor and negative if it does not. For example, blood type A positive is so called because it has both ‘A’ and Rh proteins on its surface. A person with O blood type does not have any A or B proteins on their red blood cells but may have Rh, in which case he would be an O+. If you are A+, you do not produce A nor Rh antibodies since these antibodies would attack your red blood cells.

Steps to Determine Blood Compatibility

  1. Draw blood cells of donor and recipient with antigens attached
  2. Note the antibodies that the recipient has
  3. Follow this rule to determine compatibility: The Donor cannot have an antigen that will be attacked by an antibody in the Recipient’s blood


Determine if:

  1. A- donor could donate safety to an O– recipient
  2. B+ donor could donate safely to an AB– recipient
  3. A– donor could donate safely to a B+ recipient
  4. B+ donor could donate safely to AB+ recipient


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Courtney Simons
Courtney Simons
Author, Dr. Courtney Simons has a Bachelor of Science in Food Science and a Ph. D. in Cereal Science from North Dakota State University.