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
Jehovah's Witnesses and blood transfusions and other blood-borne infections, or immune system reactions. Many physicians have expressed a willingness to respect patients' preferences and provide bloodless treatment and about 200 hospitals offer bloodless medicine and surgery programs for patients who wish to avoid or limit blood transfusions. Bloodless surgery has been successfully performed in significant procedures including open-heart surgery and total hip replacements. A 2012 study in "JAMA Internal Medicine" concluded that "Witnesses do not appear to be at increased risk for surgical complications or long-term mortality when comparisons are properly made by transfusion status. Thus, current extreme blood management strategies do not appear to