Type O-negative blood does not have any antigens. It is called the “universal donor” type because it is compatible with any blood type. Type AB-positive blood is called the “universal recipient” type because a person who has it can receive blood of any type. Although “universal donor” and “universal recipient” types may be used to classify blood in an emergency, blood type tests are always done to prevent transfusion reactions.
Minor antigens (other than A, B, and Rh) that occur on red blood cells can sometimes also cause problems and so are also checked for a match before giving a blood transfusion.
Serious transfusion reactions are rare today because of blood type tests.