Packed red blood cells do not have an antibody, since the greatest risk of Rh incompatible blood is to current or future pregnancies. For RBCs, type O negative blood is considered a "universal donor" as recipients with types A, B, or AB can almost always receive O negative blood safely. Type AB positive is considered a "universal recipient" because they can receive the other ABO/Rh types safely. These are not truly universal, as other red cell antigens can further complicate transfusions. There are many other human blood group systems and most of them are only rarely associated with transfusion problems. A screening test is
Irish Blood Transfusion Service Service. The frequency of blood groups in Ireland is as follows: It is important that the IBTS collects enough O Rh D positive blood as almost half the population are that blood type. Donors with O Rh D negative are known as universal donors. Their blood can be transfused to patients of any other blood group in an emergency or if the patient's own blood group is unavailable. Because any patient can receive O Rh D negative blood, the IBTS need to have extra O Rh D negative blood available at all times. The service depends entirely on voluntary donations