<Li> Blood group A individuals have the A antigen on the surface of their RBCs, and blood serum containing IgM antibodies against the B antigen . Therefore, a group A individual can receive blood only from individuals of groups A or O (with A being preferable), and can donate blood to individuals with type A or AB . </Li> <Li> Blood group B individuals have the B antigen on the surface of their RBCs, and blood serum containing IgM antibodies against the A antigen . Therefore, a group B individual can receive blood only from individuals of groups B or O (with B being preferable), and can donate blood to individuals with type B or AB . </Li> <Li> Blood group O (or blood group zero in some countries) individuals do not have either A or B antigens on the surface of their RBCs, and their blood serum contains IgM anti-A and anti-B antibodies . Therefore, a group O individual can receive blood only from a group O individual, but can donate blood to individuals of any ABO blood group (i.e., A, B, O or AB). If a patient in a hospital situation needs a blood transfusion in an emergency, and if the time taken to process the recipient's blood would cause a detrimental delay, O negative blood can be issued . Because it is compatible with anyone, O negative blood is often overused and consequently is always in short supply . According to the American Association of Blood Banks and the British Chief Medical Officer's National Blood Transfusion Committee, the use of group O RhD negative red cells should be restricted to persons with O negative blood, women who might be pregnant, and emergency cases in which blood - group testing is genuinely impracticable . </Li> <Table> Red blood cell compatibility table <Tr> <Th> Recipient </Th> <Th_colspan="8"> Donor </Th> </Tr> <Tr> <Th> O − </Th> <Th> O+ </Th> <Th> A − </Th> <Th> A+ </Th> <Th> B − </Th> <Th> B+ </Th> <Th> AB − </Th> <Th> AB+ </Th> </Tr> <Tr> <Th> O − </Th> <Td> Y </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Th> O+ </Th> <Td> Y </Td> <Td> Y </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Th> A − </Th> <Td> Y </Td> <Td> </Td> <Td> Y </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Th> A+ </Th> <Td> Y </Td> <Td> Y </Td> <Td> Y </Td> <Td> Y </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Th> B − </Th> <Td> Y </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> Y </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Th> B+ </Th> <Td> Y </Td> <Td> Y </Td> <Td> </Td> <Td> </Td> <Td> Y </Td> <Td> Y </Td> <Td> </Td> <Td> </Td> </Tr> <Tr> <Th> AB − </Th> <Td> Y </Td> <Td> </Td> <Td> Y </Td> <Td> </Td> <Td> Y </Td> <Td> </Td> <Td> Y </Td> <Td> </Td> </Tr> <Tr> <Th> AB+ </Th> <Td> Y </Td> <Td> Y </Td> <Td> Y </Td> <Td> Y </Td> <Td> Y </Td> <Td> Y </Td> <Td> Y </Td> <Td> Y </Td> </Tr> </Table>

Why blood group o is called universal donor