Group O individuals are known as “universal donors” because their blood can be given to any patient, regardless of their blood group. The reason for this is that the Group O red cells don’t have A or B proteins on their surface, so blood group antibodies cannot harm them. Type O blood is very useful in emergency situations when there is not time to confirm the blood group of the patient before transfusion.
Group AB individuals, on the other hand, are known as “universal recipients”. This means that they can receive any type of blood because they lack the antibodies that can react with the A and B proteins on the red cells.