People with AB positive blood are 'universal recipients' who can safely receive blood from any donor.

The ABO blood group system was first discovered by Austrian biologist Karl Landsteiner in 1901. He identified the A and B antigens, while the Rh factor was later discovered by Landsteiner and Alexander Wiener in 1937. Blood type AB positive is relatively rare, occurring in only about 3% to 4% of the United States population according to the American Red Cross.Antigens are proteins or sugars located on the surface of red blood cells that act as identification tags. If a person receives blood with foreign antigens, their immune system produces antibodies to attack the 'invader,' which can lead to a life-threatening transfusion reaction. However, individuals with AB positive blood possess both A and B antigens, as well as the Rh factor protein.Because their bodies are already familiar with all three major antigens, their plasma does not contain anti-A, anti-B, or anti-Rh antibodies. This unique biological profile allows them to accept Type A, Type B, Type AB, and Type O blood without an immune response. While they are universal recipients for red blood cells, they are actually universal donors for blood plasma.In emergency medicine, identifying these types is critical for patient safety. While AB positive patients have the most flexibility in receiving blood, hospitals still prefer to use type-specific blood whenever possible to conserve resources. This complex system of compatibility ensures that modern blood banks can manage supplies efficiently for diverse populations.