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
Blood donation blood to prepare for a disaster. The subject was discussed at length after the September 11 attacks in the United States, and the consensus was that collecting during a disaster was impractical and that efforts should be focused on maintaining an adequate supply at all times. Blood centers in the U.S. often have difficulty maintaining even a three-day supply for routine transfusion demands. The World Health Organization (WHO) recognizes World Blood Donor Day on 14 June each year to promote blood donation. This is the birthday of Karl Landsteiner, the scientist who discovered the ABO blood group system. The theme